Patent Publication Number: US-2017361993-A1

Title: Bags having composite structures and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part of prior U.S. patent application Ser. No. 11/214,419, filed on Aug. 29, 2005; is a continuation-in-part of prior U.S. patent application Ser. No. 11/214,434, filed on Aug. 29, 2005; is a continuation-in-part of prior U.S. patent application Ser. No. 11/240,944 filed on Sep. 30, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/709,512, filed on Aug. 19, 2005; and is a continuation-in-part of prior U.S. patent application Ser. No. 12/341,080, filed on Dec. 22, 2008. Each of the foregoing applications is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     Embodiments disclosed herein relate generally to bags that can be used in the packaging industry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The written disclosure herein describes illustrative embodiments that are non-limiting and non-exhaustive. Reference is made to certain of such illustrative embodiments that are depicted in the figures, in which: 
         FIG. 1  illustrates a perspective view of an embodiment of a bag having a product with a grease component disposed therein; 
         FIG. 2  illustrates a side elevation view of the bag of  FIG. 1 ; 
         FIG. 3  illustrates a perspective view of the bag of  FIG. 1  in which product is being deposited through an open end of the bag; 
         FIG. 4  illustrates a partial cross-section view of the bag of  FIG. 1  that depicts grease-resistant properties of an embodiment of a material compatible with the bag; 
         FIG. 5A  illustrates a partial exploded view of an embodiment of an outer ply compatible with the bag of  FIG. 1 ; 
         FIG. 5B  illustrates a partial exploded view of another embodiment of an outer ply compatible with the bag of  FIG. 1 ; 
         FIG. 5C  illustrates a partial exploded view of another embodiment of an outer ply compatible with the bag of  FIG. 1  in which a film portion of the outer ply is reverse printed; 
         FIG. 6A  illustrates a partial cross-sectional view of the outer ply of  FIG. 4A  taken along the view line  6 A- 6 A in  FIG. 5A ; 
         FIG. 6B  illustrates a partial cross-sectional view of the outer ply of  FIG. 5B  taken along the view line  6 B- 6 B in  FIG. 5B ; 
         FIG. 7  illustrates a partial exploded view of an embodiment of an inner ply compatible with the bag of  FIG. 1 ; 
         FIG. 8  illustrates a partial cross-sectional view of the inner ply of  FIG. 7  taken along the view line  8 - 8  in  FIG. 7 ; 
         FIG. 9  illustrates a partial exploded view of an embodiment of a material having an embodiment of an inner ply and an embodiment of an outer ply and that is compatible with the bag of  FIG. 1 ; 
         FIG. 10A  illustrates a partial cross-sectional view of the material of  FIG. 9  taken along the view line  10 A- 10 A in  FIG. 9 ; 
         FIG. 10B  illustrates a partial cross-sectional view of another embodiment of material compatible with the bag of  FIG. 1 ; 
         FIG. 11  illustrates a partial exploded view of an embodiment of material such as that of  FIG. 9  that is capable of being formed into a tube-like structure; 
         FIG. 12  illustrates a perspective view of the material of  FIG. 11  in the form of an embodiment of a tube; 
         FIG. 13  illustrates a partial perspective view of an embodiment of a closed end of a bag; 
         FIG. 14A  illustrates a cross-sectional view of the bag of  FIG. 13 , during formation of the closed end, taken along the view line  14 - 14  in  FIG. 13 ; 
         FIG. 14B  illustrates a cross-sectional view of the bag of  FIG. 14A , after formation of the closed end, taken along the view line  14 - 14  in  FIG. 13 ; 
         FIG. 14C  illustrates a cross-sectional view such as that of  FIG. 14A  of another embodiment of a closed end of a bag; 
         FIG. 14D  illustrates a cross-sectional view such as that of  FIG. 14A  of another embodiment of a closed end of a bag; 
         FIG. 14E  illustrates a cross-sectional view such as that of  FIG. 14A  of another embodiment of a closed end of a bag; 
         FIG. 15  illustrates a perspective view of another embodiment of a closed end of a bag; 
         FIG. 16A  illustrates a cross-sectional view of the closed end of the bag shown in  FIG. 15  taken along the view line  16 A- 16 A in  FIG. 15 ; 
         FIG. 16B  illustrates a cross-sectional view such as that of  FIG. 16A  of another embodiment of a closed end of a bag; 
         FIG. 17  illustrates a flow diagram that depicts a method for constructing some embodiments of the bags disclosed herein; 
         FIG. 18  illustrates a table comparing various properties of various materials, at least some of which are compatible with embodiments of a grease-resistant bag; 
         FIG. 19  illustrates a table comparing various properties of various materials, at least some of which are compatible with embodiments of a grease-resistant bag; 
         FIG. 20  illustrates a table comparing various properties of various materials, at least some of which are compatible with embodiments of a grease-resistant bag; 
         FIG. 21  illustrates a table comparing various properties of various materials, at least some of which are compatible with embodiments of a grease-resistant bag; 
         FIG. 22  illustrates a perspective view of an embodiment of a bag having a product with a grease component disposed therein; 
         FIG. 23  illustrates a side elevation view of the bag of  FIG. 22 ; 
         FIG. 24  illustrates a cutaway perspective view of an embodiment of a bag-end heat-sealing apparatus with a plurality of bags disposed thereon; 
         FIG. 25  illustrates a cutaway perspective view of an end portion of the bag of  FIG. 22 , wherein the end portion is in a closed configuration; 
         FIG. 26  illustrates a cutaway cross-section view of the end portion closed configuration as depicted in  FIG. 25  taken along the view line  26 - 26  in  FIG. 25 ; 
         FIG. 27  illustrates a flow diagram that depicts another method for constructing some embodiments of the bags disclosed herein; 
         FIG. 28  illustrates a flow diagram that depicts another method for constructing some embodiments of the bags disclosed herein; 
         FIG. 29  illustrates a perspective view of an embodiment of a bag that includes an embodiment of a composite material having multiple layers, wherein the bag has a sewn end and an open end; 
         FIG. 30  illustrates a perspective view of the bag of  FIG. 29  having a product disposed therein and two sewn ends; 
         FIG. 31  illustrates a partial cross-sectional view of a sewing needle penetrating an end portion of material during formation of an embodiment of a bag; 
         FIG. 32A  illustrates a partial cross-sectional view of a portion of an embodiment of a bag through which an embodiment of a stitching element extends; 
         FIG. 32B  illustrates a partial cross-sectional view of another portion of the bag of  FIG. 32A  through which an embodiment of a stitching element extends; 
         FIG. 33  illustrates a perspective view of a portion of an embodiment of a zipper closure at an end of an embodiment of a bag; 
         FIG. 34  illustrates a partial cross-sectional view of the zipper closure of  FIG. 14  taken along the view line  34 - 34  in  FIG. 33 ; 
         FIG. 35  illustrates a partial cross sectional view of another embodiment of a zipper closure; 
         FIG. 36  illustrates a table comparing various properties of various bags; 
         FIG. 37  illustrates a table comparing the results of drop tests performed on various bags; 
         FIG. 38  illustrates a perspective view of another embodiment of a bag constructed from an embodiment of a composite material; 
         FIG. 39  illustrates a cutaway exploded perspective view of another embodiment of a composite material from which the bag of  FIG. 38  may be formed; 
         FIG. 40  illustrates a cross-section view of the composite material of  FIG. 39  taken along the view lines  40 - 40  in  FIGS. 39 and 41 ; 
         FIG. 41  illustrates a cutaway perspective view of the composite material of  FIG. 39 ; 
         FIG. 42  illustrates a cutaway perspective view of the bottom end of the bag of  FIG. 38 ; 
         FIG. 43  illustrates a cross-sectional view of the bottom end of the bag of  FIG. 38  taken along the view line  43 - 43  in  FIG. 42 ; 
         FIG. 44  illustrates a cross-sectional view of another embodiment of a composite material compatible with embodiments of the bag of  FIG. 38 ; 
         FIG. 45  illustrates a cross-sectional view of another embodiment of a composite material compatible with embodiments of the bag of  FIG. 38 ; 
         FIG. 46  illustrates a cross-sectional view of the composite material of  FIG. 45 , wherein the material defines a closure; 
         FIG. 47  illustrates a cross-sectional view of another embodiment of a composite material; 
         FIG. 48  illustrates a cross-sectional view of an embodiment of a bag closure that includes an embodiment of the composite material of  FIG. 47 ; and 
         FIG. 49  illustrates a cross-sectional view of another embodiment of a composite material compatible with embodiments of the bag of  FIG. 38 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of bags are disclosed. In many embodiments, a bag can comprise multiple layers. Each layer can provide the bag with one or more desirable characteristics, depending on the application of the bag. In certain embodiments, the bag can comprise a paper layer, which can contribute to the stiffness of the bag and can aid in manufacturing the bag using standard converting equipment. In some embodiments, the bag can comprise one or more polyolefin and/or polyamide layers. In some embodiments, the one or more polyolefin and/or polyamide layers can provide the bag with grease-resistant properties and/or increased strength and durability. Such embodiments, as well as others, are disclosed in greater detail. 
       FIG. 1  illustrates a perspective view of an embodiment of a bag  15 . The bag  15  can include a body portion  21 , which can be substantially tubular in form. For example, the bag  15  can include a front wall  41 , a rear wall  42  a left side wall  43 , and a right side wall  44  (see also  FIGS. 2 and 3 ), which can be arranged in any suitable tubular arrangement. The body portion  21  may comprise a top end  23  and a bottom end  25 . As used herein, terms describing orientation, such as top, bottom, front, back, left, right, etc. are recited from the perspective illustrated in  FIG. 1 . Such directional terms are used for convenience and should not be construed as limiting. For example, in some embodiments, the front wall  41  may in fact be printed with material generally relegated to the back of a package, whereas the rear wall  42  may be printed with material generally displayed on the front of a package. Likewise, the top end  23  may in fact be configured for use as a base end of the bag  15 , with the bottom end  25  serving as an upper end of the bag  15 . 
     As further discussed below, the material from which the body portion  21  is formed can comprise multiple layers, each of which can provide or aid in providing desirable functional characteristics to the bag  15 . In certain embodiments, the bag  15  can have contents disposed therein, such as a product  17 . In some embodiments, the product  17  includes a grease component G. Once the product  17  is within the bag  15 , the top end  23  of the bag  15  can be closed in any suitable fashion. For example, in the depicted embodiment, each of the top end  23  and the bottom end  25  comprises a compressed lip  71 . 
       FIG. 2  illustrates a side elevation view of the bag  15  of  FIG. 1 . The tubular structure of body portion  21  may be more readily appreciated in the depiction of  FIG. 2 . The top end  23  is closed via an upper compressed lip  71 , and the bottom end  25  is closed via a lower compressed lip  71 . As described herein, the top and bottom ends  23  and  25  may be closed via any of a variety of techniques, which may employ adhesives, heat-seal films, stitches, or a combination of the preceding. For example, in some embodiments, the bag ends  23 ,  25  are not necessarily compressed in order to form a closure. 
       FIG. 3  illustrates a perspective view of the bag of  FIG. 1  in which the top end  23  is in an open configuration and the body portion  21  is receiving the product  17 . In the depiction of  FIG. 3 , lateral sides  73  are shown coupled together at a seam  75  such that the tubular shape of the body portion  21  is formed (see also  FIGS. 11 and 12  and the associated discussion below). The bottom end  25  is in a closed configuration, and in particular, is closed via a compressed lip  71 . 
     As schematically illustrated in  FIG. 4 , in some embodiments, the bag  15  can substantially prevent grease G from the product  17  from migrating or penetrating from within the bag  15  to a position outside the bag  15 . In further embodiments, the bag  15  can prevent grease at a position outside of the bag  15  from migrating into or otherwise penetrating the bag  15 . The bag  15  can also substantially block or serve as a barrier to elements other than grease, such as, for example, liquids or odors. These properties are described in further detail below. 
     With reference to  FIGS. 4-10B , in certain embodiments, the material of which the body portion  21  of the bag  15  is formed can comprise an outer ply  31  and an inner ply  51 . In some embodiments, an inner face (e.g., an inwardly facing surface) of the outer ply  31  is adhered to an outer face (e.g., an outwardly facing surface) of the inner ply  51 . In further embodiments, the inner and outer plies  51 ,  31  can be in abutting contact. For example, the inner ply  51  can be laminated to the outer ply  31 . 
     With reference generally to  FIGS. 4-6B , and more particularly to  FIGS. 5A and 6A , in certain embodiments, the outer ply  31  can comprise a film  33  and a paper layer  35 . The film  33  and the paper layer  35  can be joined in any suitable fashion. For example, the film  33  and the paper layer  35  can be laminated, such as via adhesive lamination or extrusion lamination. The film  33  can be adhered (e.g., in abutting contact) to an outer face of the paper layer  35  via a tie layer  37 . In various embodiments, the tie layer  37  can comprise a solventless adhesive, a plastic-type bonding material, or a co-extruded film. In some embodiments, the tie layer  37  comprises polyurethane. Other suitable materials are possible for the tie layer  37 . For example, solvent-based adhesives may be used. 
     Any suitable methods and equipment can be used to join the film  33  and the paper layer  35 , including those known in the art and those yet to be devised. For example, an adhesive can be applied in a conventional manner on conventional equipment. In some embodiments, the adhesive can comprise a water-adhesive in a mixture, or can comprise a 100% solids glue. For example, in some embodiments, the adhesive can comprise a radiation-cured adhesive, a solventless adhesive, a solvent-based adhesive, or a water-based adhesive. In other embodiments, extrusion coating lamination may be used. For example, in some embodiments, an extrusion coating lamination comprises the use of a PE blend as the extrudate. In some embodiments, the lamination is performed via a separate piece of equipment designed for laminating and extruding. In other embodiments, an in-line tuber is used. 
     In certain embodiments, the film  33  comprises a polyolefin, and may comprise a thermoplastic material. For example, in various embodiments, the film  33  comprises polyethylene terephthalate (PET), polyethylene terephthalate polyester (PETP), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), or polypropylene (PP). In some instances, PTT and PBT may be more expensive than PET. Certain films  33 , such as some embodiments that comprise polyester (e.g., PETP), can be puncture-resistant, tear-resistant, scratch-resistant, grease-resistant, and/or absorption-resistant. These properties can aid in providing a bag  15  with, and in maintaining, an aesthetically pleasing appearance. 
     In some embodiments, the film  33  can include one or more materials configured to provide or enhance the grease-resistance or other barrier properties of the film  33 . For example, in some embodiments, the film  33  can be resistant to or substantially impermeable to mineral oils, solvents, and acids. The film  33  can include, for example, plastics, polyvinyl chloride (PVC), polyamide (PA), polyethylene (PE), polystyrene (PS), and/or polypropylene (PP). 
     In some embodiments, the film  33  can be in a range of from about 30 gauge to about 300 gauge. In other embodiments, the thickness can be in a range from about 36 gauge to about 48 gauge. For example, in certain pet food bag applications, the film  33  can be about 48 gauge. The film  33 , however, can have other gauges for pet food bags, or for other applications, as needed or desired. 
     With reference to  FIGS. 5B and 6B , in certain embodiments, the film  33  can be treated with a coating  27  on the outer face thereof. The coating  27  can provide an enhanced barrier, and can inhibit or substantially prevent grease and/or moisture from penetrating the bag  15  from the outside. The coating  27  can protect against abrasion of the film  33 , and may provide an aesthetically appealing gloss finish. In some embodiments, the coating  27  can facilitate adhesion and bonding and can increase a coefficient of friction of the bag  15 . In some embodiments, the coating  27  can include printed indicia, which can be surface printed or reverse printed. In various embodiments, the coating  27  can comprise, for example, a flexography coating  27 , a proprietary coating  27 , or any other suitable coating  27 . For example, in some embodiments, the coating  27  can comprise the proprietary coating REPELLENCE™ barrier coating or AQUA CRYSTAL™ film coating, each of which is manufactured by Exopack, LLC of Spartanburg, S.C. 
     In some embodiments, the coating  27  can provide oil, grease, and/or water resistance without the use of traditional films and/or foils, which can be inferior for various purposes. The coating  27  can effectively preserve the quality of the package contents as well as the physical integrity of the bag  15  as a whole. For example, in some embodiments, a coating  27  that comprises REPELLENCE™ can be used with products that contain oil or grease, or for bags  15  that may occasionally be subjected to rain or other elements. In some embodiments, a coating  27  that comprises AQUA CRYSTAL™ can be relatively clear and glossy, thereby providing a bag  15  with an attractive appearance. 
     In still other embodiments, one or more additional polyolefin films  33  can be combined with the illustrated film  33 . For example, an additional polyolefin film  33  can replace the coating  27 , or in further embodiments, the additional polyolefin film can be joined with an outwardly facing surface of the illustrated film  33 , and the coating  27  can be applied to an outwardly facing surface of the additional polyolefin film  33 . 
     In certain embodiments, an outer face of the film  33  can have a coefficient of friction in a range of from about 0.5 to about 0.9. Other ranges and values are also possible. The coefficient of friction, for example, for certain pet food bag applications can be sufficiently large to inhibit slipping or sliding of a bag  15  when positioned on a shelf or cabinet. 
     With reference to  FIG. 5C , in some embodiments, an inner face of the film  33  of the outer ply  31  can include printed indicia  29 , which can aid in the identification and/or advertisement of the contents of the bag, the distributor of the bag, etc. In some embodiments, the film  33  exhibits properties (e.g., clarity, shininess, scratch resistance, etc.) that can enhance visual appearance of the bag  15 , as described above. The film  33  can be configured to transmit light such that the printed indicia  29  is visible at a position outside of the bag  15 . 
     In certain embodiments, the film  33  can be amorphous, which is a classification indicating that the film  33  is highly transparent and colorless, or can be semi-crystalline, which is a classification indicating that the film  33  is translucent or opaque with an off-white coloring. In some cases, amorphous polyester films  33  can have better ductility than semi-crystalline polyesters, but can exhibit less hardness and stiffness than the semi-crystalline type. In some embodiments, a film  33  can be printed with solvent-based inks or water based inks, and can be printed overall with a flood coat of white ink, which may allow for high-quality graphics. Certain embodiments that include a flood coat of white ink may also mask grease that might penetrate through the film  33  (e.g., via a cut or crack in the film  33 ). In some embodiments, portions of the film  33  are treated with an acrylic chemical suitable for adhering to solvent based inks, water based inks, or other inks. 
     In certain embodiments, instead of reverse printing indicia  29  on the inner face of the film  33 , indicia  29  can be surface printed on the outer face of the film  33 . It is also possible to print indicia  29  on both the inner and outer faces of the film  33 . In other embodiments, the film  33  can be unprinted (e.g., the film  33  can be substantially plain and/or clear). The film  33  can provide a bag  15  with a superior appearance, as compared with, for example, standard pet food bags. For example, a printing on the film  33  can be more aesthetically pleasing than similar printing applied to paper bags that do not have an outer film  33 . 
     With reference again to  FIGS. 4-6B  generally, in certain embodiments, the paper layer  35  of the outer ply  31  can exhibit a bending stiffness, modulus, and/or tensile stiffness that is larger than that of the film  33 . In further embodiments, the paper layer  35  can be thicker than the film  33 . In some embodiments, the paper layer  35  can provide sufficient structural rigidity to permit the bag  15  to be placed in and remain in an upright position. For example, the bag  15  might contain a product  17  in an amount sufficient to fill only a fraction (e.g., ¼, ⅓) of the bag  15 . In certain of such embodiments, the product  17  can be settled at the bottom end  25  of the bag  15 , and the bag  15  can be set upright on its bottom end  25 . Although the product  17  does not generally support the top end  23  of the bag  15  in such a configuration, the bag  15  can nevertheless remain in a substantially upright configuration, and can resist gravitational force acting on the top end  23  of the bag  15  due to the stiffness of the paper layer  35 . 
     As used herein, the term stiffness is a broad term used in its ordinary sense, and can include bending stiffness or tensile stiffness. Other suitable measurements of stiffness can also be utilized, such as droop stiffness, folding endurance, or other alternative measurements. In certain instances, bending stiffness represents the rigidity of paper or paperboard. In some cases, the bending stiffness of an item can be a function of (e.g., can be proportional to) the cube of the caliper thickness of the item. Bending stiffness can also be related to the modulus of elasticity of the item. In many embodiments, the bending stiffness of a paper layer  35  generally increases as the thickness of the paper layer  35  is increased. 
     Various instruments may be used to measure stiffness, many of which determine the stiffness of an item by subjecting it to bending of one variety or another. For example, some instruments employ 2-point bending, while others employ 4-point bending. Solid fiber boards and small fluted combined boards (which can be used in folding cartons) are typically measured with  2 -point bending instruments. Suitable instruments for measuring bending stiffness can include Taber, Gurley, and L&amp;W instruments. 
     Industry standards for measuring stiffness adopted by the Technical Association of the Pulp and Paper Industry (TAPPI) can be used to characterize the stiffness of a bag  15  or portions (e.g. layers) thereof. For example, the Gurley Stiffness value can be measured via a Gurley Stiffness Tester, manufactured by Gurley Precision Instruments of Troy, N.Y. The Gurley Stiffness Tester measures the externally applied moment required to produce a given deflection of a strip of material of specific dimensions fixed at one end and having a concentrated load applied to the other end. The results are obtained as “Gurley Stiffness” values, which can be in units of grams. 
     Similarly, stiffness can be measured in Taber Stiffness Units using a Taber® Stiffness Tester manufactured by Taber Industries of North Tonawanda, N.Y. Taber Stiffness Units can be defined as the bending moment of ⅕ of a gram applied to a 1.5 inch wide specimen at a 5 centimeter test length, flexing it to an angle of 15 degrees. Stiffness Units can be expressed in grams. 
     To obtain a reading of the Taber Stiffness of a test strip of material, the test strip can be deflected 7.5 degrees or 15 degrees in opposite directions (e.g., to the left and to the right). The average reading of the deflections can then be obtained. This average can then be multiplied using the appropriate number provided in Table A below for a particular range. The resultant product is the stiffness value of the material in Taber Stiffness Units. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE A 
               
               
                   
               
               
                   
                 Stiffness 
                 Test 
                 Roller 
                 Specimen 
                   
                 Angle of 
                 Scaling 
               
               
                 Range 
                 Units 
                 Length 
                 Position 
                 Size 
                 Weight 
                 Deflection 
                 Multiplier 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 0-1  
                 2 cm 
                 SR 
                 1½ × 1½ 
                 10 unit 
                 15° 
                 0.01 
               
               
                   
                   
                   
                 Attachment 
                   
                 compensator 
               
               
                 2 
                 0-10 
                 1 cm 
                 Up 
                 1½ × 1½ 
                 10 unit 
                 15° 
                 0.1 
               
               
                   
                   
                   
                   
                   
                 compensator 
               
               
                 3 
                 10-100 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 — 
                 15° 
                 1 
               
               
                 4 
                 50-500 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                  500 
                 15° 
                 5 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                 5 
                 100-1000 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 1000 
                 15° 
                 10 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                 6 
                 200-2000 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 2000 
                 15° 
                 20 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                 7 
                 300-3000 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 3000 
                 15° 
                 30 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                 8 
                 500-5000 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 5000 
                 15° 
                 50 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                 9 
                 1000-10000 
                 5 cm 
                 Down 
                 1½ × 2¾ 
                 5000 
                   7.5° 
                 100 
               
               
                   
                   
                   
                   
                   
                 units 
               
               
                   
               
            
           
         
       
     
     The following formula can apply to Taber Stiffness measurements: 
         E= 0.006832×(1/( w×d   3 ×θ))× S   T  
 
     where E is stiffness in flexure in pounds per square inch, w is specimen width in inches, d is the specimen thickness in inches, θ is the deflection of the specimen expressed in radians, and S T  is Taber Stiffness Units. 
     There can be a reasonable correlation between Gurley Stiffness and Taber Stiffness, such as for paperboard grades. For example, the following formula can be used to convert between Gurley Stiffness and Taber Stiffness: 
         S   T =0.01419 S   G −0.935
 
     where S T  is Taber Stiffness Units and S G  is Gurley Stiffness Units. As indicated in TAPPI Test Method T-543, paragraph 4.1.5, Gurley values can range from approximately 1.39 to 56,888 Gurley Stiffness units, and can correspond roughly to Taber values ranging from approximately 0 to 806.3 Taber Stiffness units. 
     In many embodiments, the stiffness of the paper layer  35  is selected such that the multi-layer material of which a bag  15  is ultimately formed can be laminated on existing machinery. Likewise, in many embodiments, the stiffness of the paper layer  35  is selected such that the material can be formed into the bag  15  on existing converting equipment. In some embodiments, the paper layer  35  can define a thickness in a range of between about 1.75 mils and about 10 mils, and in further embodiments, the thickness can be between about 3.0 mils and about 4.0 mils. For example, in some embodiments, the minimum thickness is about 1.9 mils. 
     In various embodiments, the film  33  can define a thickness in a range of between about 0.25 mils and about 1.25 mils, between about 0.25 mils and about 0.75 mils, or between about 0.70 mils and about 1.25 mils. In some embodiments, the film  33  can be 48 gauge and/or have a thickness in the range of about 0.475 mils to about 0.485 mils. Increased thickness of the paper layer  35  and/or the film  33  can provide for increased bending stiffness and increased stabilization of a bag  15 . In some embodiments, the film  33  can comprise PET and can define a thickness within a range of between about 0.25 mils and about 0.75 mils. In other embodiments, the film  33  can comprise BOPP and can define a thickness within a range of between about 0.70 mils and about 1.25 mils. 
     In certain embodiments, the paper layer  35  can enhance the durability of a bag  15 . Various basis weights of paper can be utilized, for example, ranging from about 30 pound-force/inch to about 50 pound-force/inch, as these units are understood by those skilled in the art. In other embodiments, the paper can be in a range between about 20 pounds per 3,000 square feet and about 80 pounds per 3,000 square feet. Embodiments of the paper layer  35  can be coated (e.g., clay-coated) and/or bleached, or in other embodiments, can be manufactured without coating or bleach. 
     In many embodiments, the paper layer  35  is substantially free of fluorocarbons. Many prior art bags include a paper constituent that has been treated with a fluorocarbon chemical, which can provide the paper with a degree of grease resistance. However, in some embodiments in which the paper layer  35  is substantially free of fluorocarbons, interior layers that are applied to the paper layer  35  (as discussed below) can provide sufficient grease resistance. 
     In other embodiments, the paper layer  35  can be treated to improve its grease-resistance. For example, in some embodiments, the paper layer  35  can be treated with a fluorocarbon chemical. Treatments (e.g., chemical treatments) other than fluorocarbon treatments are also possible, and may provide enhanced protection from grease penetrating through the paper layer  35  of the bag  15 . 
     In some embodiments, an outer face of the paper layer  35  can include printed indicia. Procedures for printing indicia can include process printing, rotogravure printing, innovative flexographic printing, etc. In some embodiments, the film  33  does not include printed indicia  29  (see  FIG. 4C ) when the paper layer  35  is printed, which can prevent the film  33  from obscuring the printed matter of the paper layer  35 . In other embodiments, both the paper layer  35  and the film  33  can include printed portions. 
     With reference generally to  FIGS. 4, 9, 10A, and 10B , in various embodiments, the inner ply  51  is adhered or otherwise joined to the outer ply  31 . As shown in  FIGS. 4, 7-9, and 10B , in some embodiments, the inner ply  51  comprises multiple layers. As shown in  FIG. 10A , in other embodiments, the inner ply  51  comprises a single layer. In either case, the inner ply  51  can be configured to resist or prevent the penetration or absorption of grease, mineral oils, solvents, and acids into or through the walls of bag  15 . The inner ply  51  can thus prevent grease within the bag  15  from contacting the paper layer  35 . 
     In some embodiments, the inner ply  51  exhibits a high degree of puncture resistance. This property can also be advantageous depending on the type of product stored in a bag  15 . For example, in some embodiments, the packed product can be relatively abrasive such that the inner ply  51  is desirably capable of withstanding the formation of pinholes during transportation and/or use of the bag  15 . 
     In some embodiments, the inner ply  51  comprises a high modulus (e.g., modulus of elasticity) such that the inner ply  51  is able to elastically stretch. When incorporated into the multi-layered material that forms the body portion  21  of a bag  15 , such an inner ply  51  can provide the bag  15  with resiliency, which can help to prevent rips, tears, or punctures. As further discussed below, in some embodiments, the resiliency afforded by the inner ply  51  can aid in sealing holes created by a sewing needle during assembly of a bag  15 . 
     With reference to  FIG. 10A , in certain embodiments, the inner ply  51  can include a single-layer or mono-layer film, which can be grease resistant or can include one or more grease-resistant components. In some embodiments, the inner ply  51  can comprise a polyolefin film layer or a laminate. For example, in certain embodiments, the inner ply  51  comprises nylon or polypropylene. In some embodiments, the inner ply  51  comprises biaxially oriented polypropylene (BOPP). In other embodiments, the inner ply  51  can comprise a material of which merely a component is nylon (e.g., a suitable polyamide) or polypropylene, and can include other materials capable of resisting grease. Some grease-resistant materials can include, for example, metalized films, ethylene vinyl alcohol, polyester, or specialty resins. In some embodiments, the grease-resistant materials provide resistance to and/or prevention of the penetration or absorption of grease, mineral oils, solvents, and/or acids. 
     In certain embodiments, the inner ply  51  comprises a single layer of polypropylene film. In various embodiments, the polypropylene inner ply  51  can exhibit relatively high grease-resistance, rigidity, translucence, chemical resistance, toughness, fatigue resistance, integral hinge properties, and/or heat resistance. Various forms of polypropylene are possible, and may be selected based on particular needs and cost considerations. For example, the inner ply  51  can comprise homopolymers, block copolymers, or random copolymers. Homopolymers, in this sense, are a general purpose grade polypropylene. Block copolymers can incorporate 5-15% ethylene and have much improved impact resistance extending to temperatures below −20 degrees C. In some instances, the toughness of block copolymers can be increased by the addition of impact modifiers, such as elastomers, in a blending process. Random copolymers can incorporate co-monomer units arranged randomly (as distinct from discrete blocks) along the polypropylene long chain molecule, typically contain 1-7% ethylene, and can be used where a relatively low melting point, relatively high flexibility, and clarity are desired. 
     In certain embodiments, the inner ply  51  comprises a single layer of nylon film. A nylon inner ply  51  can have such properties as relatively high wear and abrasion resistance, relatively high strength, and/or a relatively high modulus (e.g., modulus of elasticity). 
     With reference to  FIGS. 7-9 and 10B , in certain embodiments, the inner ply  51  includes a multi-layer film or laminate. The inner ply  51  can comprise a core layer  55  positioned between one or more films  53 ,  54 . For example, an inner face of a first film  53  can be abuttingly adhered to an outer face of a core layer  55  and/or an inner face of the core layer  55  can be abuttingly adhered to an outer face of a second film  54 . In some embodiments, the core layer  55  and the one or more films  53 ,  54  are co-extruded such that the inner ply  51  comprises at least three co-extruded layers. Other suitable laminated structures are also possible. For example, in some embodiments, the inner ply  51  comprises four or more co-extruded layers or five or more co-extruded layers. The core layer  55  can be positioned at a center of the inner ply  51  in some embodiments, and in other embodiments, can be at an off-centered position. 
     One or more of the core layer  55 , the films  53 ,  54 , and/or other layers of a ply  51  can comprise any suitable combination of the materials discussed above with respect to the single-layer inner ply  51 . In some embodiments, the core layer  55  comprises nylon or polypropylene. In other embodiments, the core layer  55  can comprise a metalized film, ethylene vinyl alcohol, polyester, or a specialty resin. In some embodiments, the core layer  55  is substantially grease-proof, is highly puncture resistant, and/or comprises a high modulus. 
     In various embodiments, one or more of the films  53 ,  54  and/or additional co-extruded layers of the inner ply  51  can comprise polyethylene, linear low density polyethylene, or metalicine. Other materials are also possible. In various embodiments, one or more of the films  53 ,  54  and/or additional co-extruded layers of the inner ply  51  can define a thickness of between about 0.5 mils and about 6.0 mils. 
     In certain embodiments, one or more of the films  53 ,  54  can be heat-sealable, which can be advantageous for certain uses of a bag  15  or in certain manufacturing procedures used to construct the bag  15 . For example, one or more of the films  53 ,  54  can be configured to melt and closingly seal at least one of the bag ends  23  and  25  in response to the application of heat. As another example, in some embodiments, an inner film  54  that is heat-sealable can be coupled to a zipper closure, as further discussed below. In certain embodiments, one or more of the films  53 ,  54  can comprise heat-sealable polyethylene (PE) or oriented polypropylene (OPP). In some embodiments, the core layer  55  can be heat-sealable. Such an arrangement can be advantageous, such as when the inner ply  51  does not include an inner film  54 . 
     In certain embodiments, the inner ply  51  defines a thickness in a range of between about 0.5 mils and about 7.0 mils. In some embodiments, the thickness is in a range of between about 2.0 mils and about 6.0 mils. Other thickness ranges or gauge values are also possible, and can depend on the use of a bag  15  into which the inner ply  51  is incorporated. For example, in some embodiments, relatively large or heavy bags (e.g., bags having a capacity of about 20 kilograms or more) can benefit from a relatively thicker inner ply  51 . Similarly, in some embodiments, bags used to store relatively sharp or abrasive products can benefit from a relatively thicker inner ply  51 . 
     Where the inner ply  51  is formed by a laminated material, the first and second films  53 ,  54  can be adhered to the core layer  55  of the inner ply  51  in any suitable manner, such as those described above with respect to joining layers of the outer ply  31 . For example, in some embodiments, the first and second films  53 ,  54  can be adhered to the core layer  55  via one or more tie layers  37 . In certain embodiments, one or more of the tie layers  37  chemically bonds the respective films  53 ,  54  to the layer  55 . For example, in some embodiments, one or more of the tie layers  37  comprises a functionalized polyethylene copolymer. The one or more tie layers  37  can comprise other suitable adhesives. 
     In some embodiments, relatively inexpensive varieties of paper can be used for the paper layer  35  in conjunction with the inner ply  51 . For example, in some embodiments, the inner ply  51  is sufficiently grease resistant to prevent grease from coming into contact with the paper layer  35 . As a result, paper that is untreated for grease resistance may be utilized, which can reduce manufacturing costs. For similar reasons, grease-resistant properties of the film  33  of the outer ply  31  can also contribute to cost savings that result from the use of paper that is not treated for grease resistance. In some embodiments, the paper used for the paper layer  35  can be selected based primarily on the stiffness and stability that it provides to the bag  15  without regard to the grease resistant properties of the paper. 
     With reference to  FIGS. 10A and 10B , in some embodiments, the outer ply  31  is joined to an outer face of the inner ply  51 . Any suitable method for joining the outer ply  31  and the inner ply  51  is contemplated, including any suitable method described above with respect to joining layers of the outer ply  31 . For example, the inner ply  51  and the outer ply  31  can be joined via co-extrusion. In some embodiments, such as those illustrated in  FIGS. 8A and 8B , the inner ply  51  and the outer ply  31  are joined via an adhesive  38 . Any other suitable lamination technique is also possible. 
     With reference to  FIGS. 11 and 12 , in some embodiments, multi-layer material formed in any of the manners described above can be converted into a bag  15 . For example, the multi-layer material can comprise an outer ply  31  joined to an inner ply  51 , and the outer and inner plies  31 ,  51  can be formed into a bag  15 . In some embodiments, the outer and inner plies  31 ,  51  can be substantially coextensive with each other, save for a protruding salvage edge. For example, in some embodiments, the outer ply  31  overlaps the inner ply  51  and is defines a surface area that is slightly larger than that of the inner ply  51  such that a portion of the outer ply  31  extends past a peripheral edge of the inner ply  51  to define a salvage edge, as this term is understood in the art. In other embodiments, the inner ply  51  can define a salvage edge. In further embodiments, the inner ply  51  can define a surface area that is larger than that of the outer ply  31 , or the inner ply  51  and the outer ply  31  can define surface areas that are substantially the same. 
     In certain embodiments, the material is cut or otherwise formed such that it has opposing lateral sides  73 . In some embodiments, the lateral sides  73  are overlapped and joined to each other to define a tubular body  21 . The lateral sides  73  can be joined in any suitable manner. For example, in some embodiments, one lateral side  73  is joined to the other lateral side  73  via an adhesive. In other embodiments, the film  33  of the outer ply  31  and the film  54  of the inner ply  51  can comprise heat-sealable materials such that the lateral sides  73  can be joined via a heat seal. In certain embodiments, a portion of the film  54  overlies a portion of the film  33  to define a seam  75 , which can extend along a full longitudinal extent of the tubular body  21 . 
     With reference to  FIGS. 13-14E , in some embodiments, a portion of at least one of the inner and outer plies  51 ,  31  of at least one of the opposing bag ends  23 ,  25  foldingly and adheringly overlies another portion of the one bag end  23  to define an overlapping seam extending along substantially an entire transverse extent of the one bag end  23  to thereby closingly seal the one bag end  23  so that a product, when positioned therein, is retained within inner confines of the bag  15  between the opposing pair of bag ends  23  and  25 . 
     Embodiments can include the inner face of the inner ply  51  of at least one of the opposing bag ends  23  adheringly overlying the outer face of the outer ply  31  of the same bag end  23  to define an overlapping seam substantially extending along a transverse extent of the bag end  23 . For example, as shown in  FIG. 14A , a flap  45  can extend downwardly from the front wall  41  beyond a bottom edge of the rear wall  42 . An inner surface of the flap  45  (e.g., the film  54  of the inner ply  51  of the flap  45 ) can be adhered to an outer surface of the rear wall  42  (e.g., to the film  33  of the outer ply  31  of the rear wall  42 ). 
     Embodiments can also include the outer face of the outer ply  31  of at least one of the opposing bag ends  23  adheringly overlying the same outer face of the same outer ply  51  of the same bag end  23  to define an overlapping seam substantially extending along a transverse extent of the bag end  23 . In certain of such embodiments, a heat seal is formed between opposing faces of the inner ply  51 . 
     Additionally, such as shown in  FIG. 14A , embodiments of a bag and/or bag closure can include an adhesive  64 . In certain embodiments, the adhesive  64  comprises a hot melt adhesive. The adhesive  64  can include components of rosin ester and ethylene vinyl acetate adhering a portion of at least one of the inner and outer plies  51 ,  31  of at least one of the opposing bag ends  23  to another portion of the same bag end  23  to define an overlapping seam substantially extending along a transverse extent of at least one of the pair of bag ends  23 . In some embodiments, the hot melt adhesive  64  can comprise Product No. 70-4467 from NATIONAL STARCH AND CHEMICAL COMPANY of Bridgewater, N.J. In other embodiments, the hot melt adhesive  64  can comprise Product No. 34-3402 or 34-3412 from Henkel Corporation of Henkel Corporation of Rocky Hill, Conn. In further embodiments, the adhesive  64  can include a component selected from the group consisting of styrene-isoprene-styrene copolymers, styrene-butadiene-styrene copolymers, ethylene ethyl acrylate copolymers, polyurethane reactive adhesives, tackifiers, waxes, paraffin, antioxidants, plasticizers, plant sterols, terpene resins, polyterpene resins, turpentines, hydrocarbon resins, resin acids, fatty acids, polymerized rosins, and polyamide adhesives. 
     Certain embodiments of the bag  15 , such as those illustrated for example in  FIGS. 14A-14D , can include a tubular bag body having a pair of opposing bag ends  23  and  25  and an inner face of an outer ply  31  abuttingly adhering to an outer face of an inner ply  51 . The outer ply  31  can include a grease-resistant film, and the inner ply  51  can include a grease-resistant material. An end portion of at least one of the inner and outer plies  51 ,  31  of at least one of the opposing bag ends  23  can adheringly overlie another portion of the same bag end  23  with an adhesive  64 , such as described above, so that the grease resistant film of the outer ply  31  contacts the adhesive  64  and the grease resistant material of the inner ply  51  contacts the adhesive  64  to thereby define an overlapping seam substantially extending along a transverse extent of the same bag end  23  to thereby closingly seal the bag end  23 . 
     With reference to  FIGS. 14A and 14B , in some embodiments, a portion of the bag  15  to which the hot melt adhesive  64  is to be applied, or with which the hot melt adhesive  64  will otherwise come into contact, is preheated. For example, in the illustrated embodiment, an inner face of the flap  45  of the front wall  41  and/or a portion of the rear wall  42  can be preheated. In some embodiments all or substantially all of an inner face of the inner ply  31  of the flap  45  can be preheated. In other or further embodiments a laterally extending strip  47  of an outer face of the outer ply  51  of the rear wall  42  can be preheated. In various embodiments, the laterally extending preheated strip  47  can extend between the sidewalls  43 ,  44  (see, e.g.,  FIGS. 1 and 3 ) so as to cover all or substantially all of the distance between the sidewalls  43 ,  44 , a majority of the distance between the sidewalls  43 ,  44 , or a minority of the distance between the sidewalls  43 ,  44 . In other or further embodiments, the laterally extending preheated strip  47  extends upwardly from a bottom edge of the rear wall  42  by a distance of no less than about 0.5 inches, no less than about 0.75 inches, or no less than about 1.0 inches. In various embodiments, the flap  45  of the front wall  41  and/or the preheated strip  47  of the rear wall  42  are preheated to a temperature within a range of from about 140 degrees Fahrenheit to about 350 degrees Fahrenheit, no less than about 140 degrees Fahrenheit, no less than about 200 degrees Fahrenheit, no less than about 250 degrees Fahrenheit, no less than about 300 degrees Fahrenheit, or about 250 degrees Fahrenheit. In some embodiments, the preheating occurs prior to compression of the portions of the flap  45  of the front wall  41  and of the rear wall  41  that contact the adhesive  64 . Preheating can be employed similarly for embodiments such as those shown in  FIGS. 14C-14E . 
     Other embodiments of the bag  15 , such as that shown in  FIG. 14E , can include a tubular bag body having a pair of opposing bag ends  23  and  25  and an inner face of an outer ply  31  abuttingly adhering to an outer face of an inner ply  51 . The outer ply  31  can include a polyester film, and the inner ply  51  can include a polymeric material. An end portion of at least one of the inner and outer plies  51 ,  31  of at least one of the opposing bag ends  23  can adheringly overlie another portion of the same bag end  23  with an adhesive  64 , such as described above, so that the polyester material of the outer ply  31  contacts the adhesive  64  and the polymeric material of the inner ply  51  contacts the adhesive  64  to thereby define a bag closure to thereby define an overlapping seam substantially extending along a transverse extent of the same bag end  23  to thereby closingly seal the bag end  23 . 
     Within the adhesives industry, hot melts, for example, can have good performance and usage benefits, as understood by those skilled in the art. Hot melt adhesives can be solvent-free adhesives that are characteristically solid at temperatures below 180 degrees F., are low viscosity fluids above 180 degrees F., and rapidly set upon cooling. Hot melt adhesives are used in a variety of manufacturing processes. There are a number of hot melt adhesives in use, with the most common being those used for hot melt pressure sensitive adhesive applications. For example, hot melt adhesives can include ethylene vinyl acetate (EVA) copolymers, which can be compatible with paraffin; styrene-isoprene-styrene (SIS) copolymers; styrene-butadiene-styrene (SBS) copolymers; ethylene ethyl acrylate copolymers (EEA); and polyurethane reactive (PUR). 
     Generally, these polymers may not exhibit the full range of performance characteristics that can be required for certain end products by themselves. For this reason, for example, a variety of tackifying resins, waxes, antioxidants, plasticizers, viscosity reducers, and other materials can be added to the adhesive formulation to enhance the polymer performance. 
     For example, the PUR adhesive is a 100 percent solid, one-component urethane prepolymer that behaves like a standard hot melt until it reacts with moisture to crosslink or chain extend, forming a new polyurethane polymer. By curing the polymer in this way, PURs have performance characteristics that can be more enhanced than those of standard hot melts. Unlike many of the other hot melts, which can require a slot die or roll coater, PURs can be applied to a substrate as a dot or a thin glue line, can set in seconds, and can be structurally rigid in minutes following a final set. These adhesives have been accepted in many manufacturing industries, for example, where they can be applied in small bond points to eliminate use of mechanical fasteners, such as staples, screws, rivets, clips, snaps, nails or stitching. 
     Furthermore, for example, certain groups of pine chemicals (with the exception of plant sterols, in many instances), can also be used by the adhesives and sealants industry. Pine chemicals are renewable, naturally occurring materials derived from the pine tree (genus  pinus ). The range of chemical classes obtained from pine trees includes numerous plant sterols, terpenes (or turpentine), resin acids (or rosin) and fatty acids. Rosin resins, including esters and polymerized rosins, are used as tackifiers to modify the properties of selected polymers to produce adhesives and sealants. Polyterpene resins are used to modify non-polar polymers for these same applications. Tall oil fatty acids can be dimerized to produce dimer fatty acids that, in turn, can be a major ingredient in thermoplastic polyamide adhesives. 
     For example, three major classes of tackifier resins for the adhesives industry can include terpene, hydrocarbon and rosin resins. Terpene resins (pine-based) and hydrocarbon resins (petrochemical-based) are both hydrocarbons; that is, they contain only carbon and hydrogen. Although they are somewhat similar in that respect, they impart somewhat different properties to the resultant adhesives. Terpene-based resins are more diverse than petrochemical hydrocarbons in that these resins can be readily modified with other chemicals (e.g., phenol) to produce an array of products. Notably, for example, rosin resins significantly differ from the previous two types in that they contain carboxylic acid and/or ester groups. These resins are generally more polar and narrower in molecular weight, for example, making them good tackifiers for a variety of end-use applications. 
     In some instances, hot-melt packaging adhesives can be developed to run faster than traditional adhesives, in some applications, and can perform on a range of substrates. Terpene phenolic resins, derivatives of alpha-pinene, can deliver enhanced adhesion qualities to difficult substrates such as recycled cardboard. They can offer better green strength, making them useful for high-speed packaging lines with short set times. Rosin esters are commonly used to increase adhesion and the temperature performance range of ethylene vinyl acetate (EVA) based adhesives. This combination of elements in a hot melt adhesive can be used as a closure (e.g., end, sides, or other overlap region) for a bag in applications, for example, of a polyester or grease-resistant material facing another polymeric or grease resistant material. Rosin esters can be compatible with a range of polymers, thus limiting formulating complexity. 
     Ethylene vinyl acetate (EVA), for example, can be produced by the random copolymerization of ethylene and vinyl acetate in predetermined ratio. The presence of VA reduces the crystallinity as the large acetoxy group distorts the chain structure. The stiffness of EVA varies with VA content. However, beyond about 60 percent VA, the stiffness rises sharply as pure vinyl acetate is a glass-like substance at room temperature. The practical limit for certain “mechanical” uses of EVA is about 20 percent VA content; however, for certain “adhesive” uses, higher levels of VA can be employed. High VA level copolymers are typically used in adhesive applications, while lower vinyl acetate containing copolymers, which can have greater tensile moduli and surface hardness, find greatest use in films, profile extrusions and injection molding. The higher percent VA resins have a good compatibility with other materials. Thus, EVA is widely used in blends and compounds. One main application, for example, is hot melt adhesives, where the EVA is blended with tackifier and paraffin wax. 
     As understood by those skilled in the art, the polarity of the VA molecule makes the copolymers receptive to high filler loadings and to combination with tackifiers and other adhesive components. The addition of the rosin ester to EVA can produce a compatible mixture. The increase in the VA amount decreases the crystallinity of EVA and the elastic and viscous modules, but increases the peel strength and the tack. The tackifier improves the adhesion and increases the “open time” of the formulation. 
     In a further embodiment in which one or more bag ends or other bag closures are heat-sealed, a bag end  23  is adapted to be positioned so that opposingly facing first and second portions of the inner ply  51  are compressed between opposingly facing first and second portions of the outer ply  31  to define a compressed lip  71 , as shown in  FIGS. 15-16B . The compressed lip  71 , for example, can have a first portion of the second heat-sealable film  54  of the inner ply  51  meltingly bonded with an opposingly facing second portion of the second heat-sealable film  54  of the inner ply  51  along a transverse extent of at least one of the pair of bag ends  23  and  25  responsive to heat applied thereto. Application of the heat to the bag end  23  thereby closingly seals the bag end  23  so that a food element  17 , when positioned therein, is retained within inner confines of the bag  15  defined by other unsealed portions of the second heat-sealable film  54  positioned between the opposing bag ends  23  and  25 .  FIG. 3  shows an embodiment of a bag where the food element  17  is positioned inside the bag, illustrating the grease component G being prevented from penetrating the inner and outer plies  51 ,  31  of the food bag  15 . 
     Each of the materials used to construct the bag  15  can have a different range of melting temperatures. For example, in some embodiments, a polyester film  33  of the outer ply  31  has a melting point temperature greater than a heat-sealable film  54  of the inner ply  51 . In one embodiment, the polyester film  33  of the outer ply  31  has a melting temperature in the range of about 300 degrees Fahrenheit to about 475 degrees Fahrenheit, and preferably greater than 425 degrees Fahrenheit. In one embodiment, the heat-sealable film  54  of the inner ply  51  has a melting point temperature in the range of about 220 degrees Fahrenheit to about 300 degrees Fahrenheit, and preferably greater than 240 degrees Fahrenheit. As understood by those skilled in the art, the polyethylene heat-sealable film  54  of the inner ply  51  has a lower melting temperature and therefore melts easier and at lower temperatures than the grease-resistant polyester film  33  of the outer ply  31 . A sufficiently low melting point temperature for the heat-sealable film  54  of the inner ply  51  allows for the melting and bonding of the second heat-sealable film  54  to closingly seal the bag end  23  and  25 . 
     For example, as understood by those skilled in the art, heat-sealing bag machine performs the function of forming and shaping the multi-layered structure into a bag  15  by accordingly compressing and melting the bag ends  23  and  25  to closingly seal the bag ends  23  and  25 . The heat-sealing bag machine has an extended heater belt and/or heated jaws that carry out the heat-sealing procedure. The heat can alternatively be applied, for example, by heated rollers, heated wire/wires, or a heated air zone that adequately melts the heat-sealable film  54 , as understood by those skilled in the art. The extended heater belt and/or heated jaws can mass-produce the heat-sealed products through a continuous high-speed operation, which manufactures a quality product in massive quantities to be delivered to customers. In some applications, for example, the bag manufacturer typically heat-seals one end of each bag and delivers the bag to a customer, and the customer fills the bag with the proper elements and ultimately heat-seals the other end of the bag. The heat-sealing process can form bags with a lip as herein described, or can alternatively form bags that have a flattened top end and flattened bottom end to thereby provide the capability of stacking multiple bags neatly on top of one another. 
     To describe heat-sealing processes for certain embodiments more specifically, the polyethylene portion of the heat-sealable film  54  of the inner ply  51  at the bag ends  23  and  25  can be heated to a melting point temperature of at least 220 degrees Fahrenheit to melt the heat-sealable polyethylene film of the bag ends  23  and  25 . Alternatively, the temperature could be raised in excess of 300 degrees Fahrenheit, in one embodiment for example, to melt not only portions of the polyethylene heat-sealable films  54  together but also to melt portions of the polyester films  33  together as well, thus forming an even tighter closed seal at the bag ends  23  and  25 . In one embodiment, for example, the manufacturer utilizing the heat-sealing bag machine will seal only one end  23  and  25  portion of the bag  15 , thereby leaving another end  23  and  25  portion of the bag  15  open to eventually fill the bag  15  with food or other elements  19 . The distributor of the goods, for example, then fills the bag  15  with the food or other elements  19 , and thereafter seals the other end  23  and  25  portion of the bag  15  after the bag  15  is full. 
       FIG. 17  illustrates a schematic diagram of an embodiment of a method for constructing a composite bag, as disclosed herein. Other embodiments of methods of assembling, positioning, using, and constructing a multi-layered bag  15  are also disclosed herein. The following discussion includes specific references to certain of such embodiments. The discussion is for illustrative purposes only, and should not be construed as limiting. Moreover, any suitable combination of the following disclosure with any portion of the foregoing disclosure is contemplated. 
     In certain embodiments, before any of the layers of a tube-forming material are bonded or adhered together, the method of constructing a bag  15  can include printing printed indicia  29  on the inner face of the grease-resistant film  33  of the outer ply  31  to enhance visual appearance of the bag  15 . Also, before adhering the layers of film, the method can include clay-coating and bleaching the paper layer  35 , and treating the paper layer  35  with a chemical to provide enhanced protection from grease penetrating through the paper layer  35  of the bag  15 . 
     In certain embodiments, a method of constructing a bag  15  can include adhering an inner face of a grease-resistant polyester film  33  with an outer face of a paper layer  35  to create an outer ply  31 . The method can also include adhering an inner face of a first film  53  to an outer face of a grease-resistant material  55  and adhering an inner face of the grease-resistant material  55  to an outer face of a second film  54  to create a multi-layer inner ply  51 . The method can also include adhering an inner face of the outer ply  31  to an outer face of the inner ply  51  to create a laminate with a pair of opposing ends  23  and  25 . The method can also include overlying a portion of an inner face of the inner ply  51  located at one lateral side of the laminate onto a portion of an outer face of the outer ply  31  located at another lateral side of the laminate to define an overlapping seam extending along a longitudinal extent of a tubular portion of the bag. The method can also include adheringly overlying an end portion of at least one of the inner and outer plies  51 ,  31  of at least one of the opposing bag ends  23  onto another portion of the same bag end  23  with an adhesive  64  including components of rosin ester and ethylene vinyl acetate to define an overlapping seam substantially extending along a transverse extent of the same bag end  23  to thereby closingly seal the bag end  23 . 
     In some embodiments, an inner face of the inner ply  51  of at least one of the opposing bag ends  23  is adhered to an outer face of the outer ply  31  of the same bag end  23  to define an overlapping seam substantially extending along a transverse extent of the bag end  23 . The method can further include closingly sealing the overlapping seam responsive to the adhering to thereby prevent grease from penetrating from within the bag  15  to outside the bag  15  and prevent grease from penetrating from outside the bag  15  to within the bag  15 . 
     The method can also include adhering an outer face of the outer ply  31  of at least one of the opposing bag ends  23  against the same outer face of the same outer ply  31  of the same bag end  23  to define an overlapping seam substantially extending along a transverse extent of the bag end  23 . The method can further include closingly sealing the overlapping seam responsive to the adhering to thereby prevent grease from penetrating from within the bag  15  to outside the bag  15  and prevent grease from penetrating from outside the bag  15  to within the bag  15 . 
     Certain embodiments of bags and methods herein disclosed can have important benefits and advantages. The combined use of polymeric structures and paper, for example, can combine the advantages of the thickness and bending stiffness of paper with the puncture-resistant and grease-resistant properties of polyester, including in some embodiments the heat-sealable characteristics of films such as polyethylene. Furthermore, the grease-resistant properties of the inner ply  51  can offer enhanced grease-resistance in addition to the grease-resistance properties of the outer ply  31 . Embodiments of a bag can provide increased barrier protections from grease, endurance, strength, physical integrity, and heat-sealable characteristics not offered with other bags. The bag  15  can prevent problems customarily associated with greasy products such as pet food, for example, and eliminate the absorption and penetrable effect of the grease component included in such foods as pet food. Various bags  15  are often used in other settings where greasy elements are contained within the bags  15 , and embodiments of the bag contribute to solving such problematic concerns attributable to the grease. Other applications of the bag  15  may include dry foods, beverages, feed, soil, lawn and garden, building materials, and other markets to prevent grease from penetrating from outside the bag  15  to within the bag  15  and to prevent grease from penetrating from within the bag  15  to outside the bag  15 . Furthermore, certain embodiments can offer enhanced strength to allow the bag to carry over twenty-five pounds of pet food with relative ease. 
     In some embodiments, materials used in constructing a bag can be environmentally friendly, in that the resulting bag is less toxic and increasingly biodegradable. Further, in some embodiments, a bag  15  can be manufactured on existing equipment, such that investment in new and expensive bag manufacturing equipment is unnecessary. 
     As discussed above, a variety of bag styles are possible. For example, in various embodiments, the bag  15  can comprise a gusseted pinch-bottom bag configuration, a non-gusseted pinch-bottom bag configuration, other various pinch-bottom bag configurations, and various block-bottom configurations. As previously discussed, the bag-end closures can be substantially grease-resistant or grease-proof so as to substantially prevent grease from exiting the bag via the closed ends. 
       FIGS. 18-20 , which contain Tables 1-3, illustrate comparisons of different illustrative examples of an outer ply  31  and inner ply  51  construction, as compared with other materials, in such categories as stiffness, puncture resistance, tear resistance, and tear initiation.  FIG. 21 , which contains Table 4, illustrates raw data utilized in the calculations of tables 1-3 of  FIGS. 18-20 . The data from Table 4 of  FIG. 21  includes properties of various materials and multi-layer combinations of materials. The raw data of Table 4 of  FIG. 21  illustrate advantages that are possible with multi-layer combinations. 
     Many different grades and gauges for the PET, paper, and film are possible.  FIGS. 18-21  illustrate certain advantages that can result from non-limiting examples of body materials having a multi-layer structure, which include, for example, enhanced stiffness, puncture resistance, tear resistance, and/or tear initiation. 
     Abbreviations are used in Tables 1-4. In particular, CSR4 (i.e., tradename CSR4) represents a type of fluorocarbon treated, clay coated, bleached sheet of paper; MWK represents a type of multi-wall Kraft (MWK) brown paper; Trial BL Non-CC represents type of fluorocarbon treated, bleached (BL) sheet of paper that is non-clay-coated (Non-CC); W-RPSE represents a type of Royal Performance semi-extensible (RPSE) white paper; Ad One (i.e., Advantage One) represents a type of substrate of a heavy extensible sheet of paper; 65# BL-MWK represents a bleached (BL) multi-wall Kraft (MWK) sheet of paper having a basis weight of 65 lbs; 48 gauge PET represents a PET layer of 48 gauge; and 2.5 mil. FT 2510 coextruded film represents a nylon coextruded core film having a 2.5 mil. gauge and a 2510 grade specification. Furthermore, in Tables 1-4 in  FIGS. 18-21 , references to paper correspond to the paper layer  35  of the outer ply  31 , references to PET correspond to the outer layer  33  of the outer ply  31 , and references to FT 2510 coextruded film correspond to the multi-layer or mono-layer formation of the inner ply  51 . 
       FIG. 18  illustrates the percent increase in machine-direction tensile stiffness and cross-direction tensile stiffness, as these measurements are understood by those skilled in the art, for the following illustrative comparisons: 48 gauge PET, CSR4 paper, and 2.5 mil. FT 2510 coextruded film v. PET; 48 gauge PET, CSR4 paper, and 2.5 mil. FT 2510 coextruded film v. 2.5 mil. FT 2510 coextruded film; 48 gauge PET, Advantage One paper, and 2.5 mil. FT 2510 coextruded film v. PET; and 48 gauge PET, Advantage One paper, and 2.5 mil. FT 2510 coextruded film v. 2.5 mil. FT 2510 coextruded film. 
       FIG. 19  illustrates the percent increase in dull-puncture and sharp-puncture, as these measurements are understood by those skilled in the art.  FIG. 20  illustrates the percent increase in machine-direction tear resistance and cross-direction tear resistance, as these measurements are understood by those skilled in the art.  FIG. 20  also shows the percent increase in machine-direction tear initiation and cross-direction tear initiation, as these measurements are understood by those skilled in the art. Each of the tables in  FIGS. 18-20  illustrates data relating to the following illustrative comparisons: 48 gauge PET v. paper; and 48 gauge PET and 2.5 mil. FT 2510 coextruded film v. paper. 
       FIG. 22  illustrates a perspective view of another embodiment of a bag  115 . The bag  115  can resemble the bag  15  in many respects, thus like features are identified with like reference numerals, incremented by  100 . Any suitable feature of the various embodiments of bag  15  can be incorporated into or otherwise used with the bag  115 , and any suitable feature of the various embodiments of the bag  115  can be incorporated into or otherwise used with the bag  15 . Further, the bag  115  may be assembled and/or used according to any suitable method, such as any suitable method discussed above with respect to the bag  15 . 
     The bag  115  can include a body portion  121 , which can be substantially tubular in form. The body portion  121  may comprise a top end  123  and a bottom end  125 . As further discussed below, the material from which the body portion  121  is formed can comprise multiple layers, each of which can provide or aid in providing desirable functional characteristics to the bag  115 . In certain embodiments, the bag  115  can have contents disposed therein, such as a product  117 . In some embodiments, the product  117  includes a grease component G. Once the product  117  is within the bag  115 , the top end  123  of the bag  115  can be closed in any suitable fashion. For example, in the depicted embodiment, each of the top end  123  and the bottom end  125  is heat sealed at or along a compressed lip  171 . 
       FIG. 23  illustrates a side elevation view of the composite bag  115  of  FIG. 21 . The tubular structure of body portion  121  may be more readily appreciated in the depiction of  FIG. 23 . The top end  123  is closed via an upper compressed lip  171 , and the bottom end  125  is closed via a lower compressed lip  171 . As described herein, the top and bottom ends  123  and  125  may be closed via a variety of techniques, which may employ adhesives, heat-seal films, stitches, or a combination of the preceding. For example, in some embodiments, the bag ends  123 ,  125  are not necessarily compressed in order to form a closure. 
     The body portion  121  may be similar to body portion  21  described above. For example, various embodiments of the body portion  121  may comprise a structure that is substantially the same as that of any suitable embodiment of the body portion  21 . For example, body portion  121  may comprise a composite material that includes an outer ply  131  joined to an inner ply  151  (see  FIG. 26 ). The outer and inner plies  131 ,  151  can be substantially the same as one or more embodiments of the outer and inner plies  31 ,  51  described above. 
     In the embodiments of bag  115  depicted in  FIGS. 22-28 , the inner ply  131  comprises one or more layers of heat-sealable film  153 ,  154 , which can resemble embodiments of the heat-sealable films  53 ,  54  described above. As described below, heat-sealable layers may be employed to close and seal one or more of the ends  123 ,  125  of bag  115 . 
     As shown in  FIGS. 24-26 , each of the pair of bag ends  123  and  125  is configured to be positioned so that opposingly facing first and second portions of the inner ply  151  are compressed between opposingly facing first and second portions of the outer ply  131  to define a compressed lip  171 . The compressed lip  171 , for example, can have a first portion of the second heat-sealable film  154  of the inner ply  151  meltingly bonded with an opposingly facing second portion of the second heat-sealable film  154  of the inner ply  151  along a transverse extent of at least one of the pair of bag ends  123  and  125  responsive to heat applied thereto. Application of the heat to the bag end  123  and  125  thereby seals at least one of the pair of bag ends  123  and  125  so that a product, when positioned therein, is retained within inner confines of the bag  115 , which may be defined by unsealed portions of the second heat-sealable film  154  that extend between the opposing bag ends  123  and  125 . 
     Each of the materials used to construct the bag  115  can have a different range of melting temperatures. The polyester film  133  of the outer ply  131 , for example, may have a melting point temperature greater than the heat-sealable film  154  of the inner ply  151 . In one embodiment, the polyester film  133  of the outer ply  131  has a melting temperature in the range of about 300 degrees Fahrenheit to about 475 degrees Fahrenheit, and preferably greater than 425 degrees Fahrenheit. In one embodiment, the heat-sealable film  154  of the inner ply  151  has a melting point temperature in the range of about 220 degrees Fahrenheit to about 300 degrees Fahrenheit, and preferably greater than 240 degrees Fahrenheit. As understood by those skilled in the art, the polyethylene heat-sealable film  154  of the inner ply  151  has a lower melting temperature and therefore melts easier and at lower temperatures than the grease-resistant polyester film  133  of the outer ply  131 . A sufficiently low melting point temperature for the heat-sealable film  154  of the inner ply  151  allows for the melting and bonding of the heat-sealable film  154  to close and seal the bag ends  123  and  125 . 
     In certain embodiments, a heat-sealing bag machine performs the function of forming and shaping the multi-layered structure into a bag  115  by compressing and melting the bag ends  123  and  125  so as to closingly seal the bag ends. The heat-sealing bag machine can include an extended heater belt and/or heated jaws that carry out the heat-sealing procedure. The heat can alternatively be applied, for example, by heated rollers, heated wire/wires, or a heated air zone that adequately melts the heat-sealable film  153 . The extended heater belt and/or heated jaws can mass-produce the heat-sealed products through a continuous high-speed operation, which manufactures a quality product in massive quantities to be delivered to customers in the ordinary course of business, as shown for example in  FIG. 24 . The bag manufacturer can heat-seal one end of each bag and deliver the bags to an intermediate customer, and the customer fills the bag with the desired elements and ultimately heat-seals the other end of the bag. The heat-sealing process can form bags with a lip as herein described, or can alternatively form bags that have a flattened top end and flattened bottom end to thereby provide the capability of stacking multiple bags neatly on top of one another. 
     To describe embodiments of the heat-sealing process more specifically, for example, the polyethylene portion of an embodiment of the heat-sealable film  154  of the inner ply  151  at the bag ends  123  and  125  can be heated to a melting point temperature of at least 220 degrees Fahrenheit, in one embodiment for example, to melt the heat-sealable polyethylene film of the bag ends  123  and  125 . Alternatively, the temperature could be raised in excess of 300 degrees Fahrenheit to melt not only portions of the polyethylene heat-sealable films  154  together but also to melt portions of the polyester films  133  together, which may produce an even tighter closed seal at the bag ends  123  and  125 . 
     As illustrated in  FIGS. 22-28 , and especially  FIGS. 27 and 28 , the present disclosure also includes embodiments of methods of assembling, positioning, using, and constructing a multi-layered bag  115 . For example, in some embodiments, before any of the layers are bonded or adhered together, a method of constructing a bag  115  can include printing printed indicia on the inner face of the grease-resistant film  133  of the outer ply  131  to enhance visual appearance of the bag  115 . Also, before adhering the layers of film, the method can include clay-coating and bleaching the paper layer  135 . In some embodiments, the method can include treating the paper layer  135  with a chemical to provide enhanced protection from grease penetrating through the paper layer  135 , while in other embodiments, the paper layer  135  is untreated. 
     In certain embodiments, a method can include adhering an inner face of a grease-resistant film  133  with an outer face of a paper layer  135  to create an outer ply  131 . The method can include applying a tie layer  37  (see, e.g.,  FIG. 4 ) between the inner face of the grease-resistant film  133  of the outer ply  131  and the outer face of the paper layer  135  to attach the grease resistant-film to the paper layer  135 . The method can also include adhering a grease-resistant material  155  between a pair of heat-sealable films  153 ,  154  to create a multi-layer inner ply  151  by adhering an inner face of a first of the pair of heat-sealable films  153 ,  154  to an outer face of the grease-resistant material  55  and adhering an inner face of the grease-resistant material  155  to an outer face of a second of the pair of heat-sealable films  153 ,  154 , and applying tie layers (e.g., of solvent-based petroleum distillate) between the grease-resistant material  155  of the inner ply  151  and the pair of heat-sealable films  153 ,  154  to adhere the grease-resistant film  133  between the pair of heat-sealable films  153 ,  154 . 
     Other embodiments of the methods disclosed herein include adhering an inner face of the outer ply  131  to an outer face of the inner ply  151  to create a laminate with a pair of opposing ends  123  and  125 . Also, for example, the method can include providing a coating  127  to the outer face of the grease-resistant film  133  of the outer ply  131 , which can provide enhanced protection from grease penetrating from outside the bag  115  to within the bag  115 . The method can further include cutting each of the pair of opposing ends  123  and  125  so that the outer ply  131  has a substantially similar longitudinal length from one bag end  123 ,  125  to the other bag end  123 ,  125  along a circumferential periphery of each of the pair of opposing bag ends  123 ,  125  and the inner ply  151  has a substantially similar longitudinal length from one bag end  123 ,  125  to the other bag end  123 ,  125  along the circumferential periphery of each of the pair of opposing bag ends  123 ,  125 , and overlying a portion of an inner face of the inner ply  151  located at one lateral side  173  of the laminate onto a portion of an outer face of the outer ply  131  located at another lateral side  173  of the laminate to define an overlapping seam  175  extending along a longitudinal extent of a tubular portion of the bag  115 . 
     Embodiments of the methods disclosed herein can further include melting opposing faces of at least one of the pair of heat-sealable films  153 ,  154  together along a transverse extent of at least one of the pair of ends  123 ,  125  responsive to heat being applied thereto, and compressing opposingly facing first and second portions of the inner ply  151  between opposingly facing first and second portions of the outer ply  131  at a location of at least one of the pair of ends  123 ,  125  along a transverse extent to thereby define a compressed lip  171 , and closingly sealing at least one of the pair of ends  123 ,  125  responsive to the melting without overlapping any portion thereof so that a grease element  117 , when positioned therein is, retained between other portions of the inner ply  151  remaining unmelted and unsealed, which can prevent grease from penetrating from within the bag  115  to outside the bag  115  and prevent grease from penetrating from outside the bag  115  to within the bag  115 . 
       FIG. 29  illustrates a perspective view of another embodiment of a bag  215 . The bag  215  can resemble the bags  15 ,  115  in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “2”. Any suitable feature of the various embodiments of bags  15 ,  115  can be incorporated into or otherwise used with the bag  215 , and any suitable feature of the various embodiments of the bag  215  can be incorporated into or otherwise used with the bags  15 ,  115 . Further, the bag  215  may be assembled and/or used according to any suitable method, such as any suitable method discussed above with respect to the bags  15 ,  115 . 
     The bag  215  can include a body portion  221 , which can be substantially tubular in form. In some embodiments, the body portion  221  defines a front wall  201 , a back wall  202 , a first side wall  203 , and a second side wall  204 . In certain embodiments, the bag  215  defines a sewn-open-mouth configuration, and can include a closure seam  210  at a bottom end  225  of the body portion  221 . In some embodiments, the seam  210  comprises one or more stitching elements  211 , such as threads, strings, or yarns, which extend through the front wall  201  and the back wall  202  in a sewn or stitching pattern. In some embodiments, the one or more stitching elements  211  can further extend through end portions of the first side wall  203  and/or the second side wall  204 . In some embodiments, a closure strip  212 , which can comprise paper or any other suitable material, is positioned over (e.g., at an outwardly facing surface of) the front wall  201  and the back wall  202  and is sewn to the front and back walls  201  and  202  via the one or more stitching elements  211 . When the bag  215  is in a sewn-open-mouth configuration, a top end  223  of the bag  215  can be open such that a product can be received into the bag  215 , and the product can be maintained within the bag  215  via the closed bottom end  225 . 
     In some embodiments, the body portion  221  comprises a sheet of material that is folded or otherwise formed into the substantially tubular structure. The body portion  221  may resemble the body portions  21 ,  121  described above. For example, various embodiments of the body portion  221  may comprise the same structure as any of the embodiments of the body portions  21 ,  121 , such as those depicted and described in  FIGS. 4-12 and 26  and the associated written disclosure. For example, the body portion  221  may comprise a composite material with an outer ply  231  and an inner ply  251  (see, e.g.,  FIG. 31 ). The outer and inner plies  131 ,  151  can be substantially the same as one or more embodiments of the outer and inner plies  31 ,  51 ,  131 ,  151  described above. 
     With reference to  FIG. 30 , in certain embodiments, the bag  215  can have contents disposed therein, such as a product  217 . In some embodiments, the product  217  includes a grease component G. Once the product  217  is within the bag  215 , the top end  223  of the bag  215  can be closed in any suitable fashion. For example, the illustrated embodiment includes a closure seam  213  such as the closure seam  210  at the bottom end  225  of the bag  215  (discussed above). 
     With reference to  FIGS. 29 and 30-32A , in certain embodiments, at least one end  223 ,  225  of a tubular body  221  (such as, for example, the tubular body  21  depicted in  FIG. 12 ) can be sewn closed to provide a bag  215  in a sewn-open-mouth configuration (e.g., having a first end that is sewn closed and a second end that is open). In some embodiments, the bottom end  225  of the bag  215  comprises a closure seam  210  and the top end  223  is left open such that a product can be received into the bag  215  via the top end  223 . 
     With reference to  FIG. 31 , in some embodiments, a method of forming the bag  215  into a sewn-open-mouth configuration includes urging the front wall  201  and the back wall  202  of the tubular body  221  toward one another. Although each of the front and back walls  201  and  202  in the illustrated embodiment comprise three layers (i.e., a two-layered outer ply  231  and a single-layered inner ply  251 ), any suitable layered arrangement disclosed herein is possible. As shown in  FIG. 30 , the front wall  201  and the back wall  202  can be placed in abutting contact with each other. In further embodiments, a closure strip  212  is placed over the bottom end  225  of the front and back walls  201  and  202 . For example, the closure strip  212  can be folded or bent such that a portion of the closure strip  212  contacts an outer surface of the front wall  201  and another portion of the closure strip  212  contacts an outer surface of the back wall  202 . 
     With reference to  FIGS. 31 and 32A , in some embodiments, a stitching element  211  is introduced into a bottom region of the tube body  221  via a stitching needle  205 . The stitching needle  205  can be configured to pierce through a first portion of the closure strip  212 , the front wall  201 , the back wall  202 , and a second portion of the closure strip  212 . The stitching needle  205  thus can form openings  206  in the closure strip  212 , an opening  207  in the front wall  201 , and an opening  208  in the back wall  202 . 
     In some embodiments, the stitching needle  205  carries the stitching element  211  through the openings  206 ,  207 , and  208  and positions a portion of the stitching element  211  within the openings  206 ,  207 , and  208 . Accordingly, upon removal of the stitching needle  205  from the bottom end  225  of the tube body  221 , the stitching element  211  can extend through the openings  206 ,  207 , and  208  in a substantially fixed state. 
     The stitching element  211  can hold the front wall  201  and the back wall  202  in close engagement with one another so as to form a substantially grease-impermeable seal. As used herein the term grease-impermeable seal is used in its ordinary sense, and can include a seal that prevents the passage of grease thereby. Accordingly, a substantially grease-impermeable seal formed at a bottom end  225  of a bag  215  can substantially prevent grease from entering or exiting the bag  225  via the bottom end  225 . As illustrated in  FIG. 29 , in some embodiments, the stitching element  211  can extend across a full transverse width of the bag  215  (e.g., from one lateral edge of the front wall  201  to an opposing lateral edge of the front wall  201 ), and can form a substantially grease-impermeable seal along the full transverse width of the bag  215 . In further embodiments, the substantially grease-impermeable seal can also substantially prevent the passage of odors via the seal. 
     In some advantageous embodiments, the front and back walls  201 ,  202  are configured to close around the stitching element  211  upon removal of the stitching needle  205 . For example, in some embodiments, the memory of the inner ply  251  (or a portion thereof, such as a core layer  255 ) is sufficiently large to permit the inner ply  251  to elastically deform as the stitching needle  205  passes through it. Upon removal of the needle  205 , the inner ply  251  can move toward a more relaxed, more natural, or more constricted configuration and can close around the stitching element  211 . The inner ply  251  can contact, constrict, or otherwise interact with the stitching element to form a substantially grease-impermeable seal. In some embodiments, a substantially grease-impermeable seal formed between the front and back walls  201 ,  202  and the stitching element  211  at the openings  206  and  207  can substantially prevent the passage of odors via the seal. 
     In some embodiments, the outer ply  231  can form, or contribute to the formation of, a substantially grease-impermeable seal between the front and back walls  201  and  202  and the stitching element  211 . For example, in some embodiments, the memory of the outer ply  231  (or a portion thereof, such as the film  233 ) is sufficiently large to permit the outer ply  231  to elastically deform as the stitching needle  205  passes through it and to move toward a more constricted state upon removal of the needle  205 . 
     In some embodiments, the memory of a material is affected by the thickness of the material. The term “memory” is used herein in its ordinary sense, and can include a property of the material by which the material can be stretched from a first position to a second position, and upon release from the second position, can completely return, or can return by a percentage amount, to the first position. By way of example, in some instances, PET films have a relatively low memory and PE films have a relatively high memory. In many instances, the memory of a material increases as the thickness of the material increases. In various embodiments, the thickness of the inner ply  251 , or a portion thereof (e.g., the core layer  255 ), is between about 1 mils and about 6 mils, between about 2 mils and about 5 mils, or between about 3 mils and about 4 mils. In various embodiments, the thickness of the outer ply  233 , or a portion thereof (e.g., the film  233 ), is between about 1 mils and about 6 mils, between about 2 mils and about 5 mils, or between about 3 mils and about 4 mils. 
     In certain embodiments, the stitching element  211  can comprise a material configured to interact with one or more materials of the front and back walls  201  and  202  to form a substantially grease-impermeable seal therewith. In various embodiments, the stitching element can comprise cotton, a polyolefin, and/or a blend of synthetic materials and cotton. 
     As illustrated in  FIGS. 29 and 32B , in certain embodiments, a bag  215  can be formed with gusseted sidewalls  203  and  204 . With reference to  FIG. 12 , in some embodiments, the sidewalls of a substantially tubular body can be urged inward to form the gussets, as depicted by block arrows, and can be creased or folded. With reference to  FIG. 32B , in some embodiments, the stitching element  211  can extend through two separate portions of a gusseted side wall (e.g., the side wall  203 ). In the illustrated embodiment, the front wall  201  defines the opening  207 , the back wall defines the opening  208 , a first portion of the side wall  203  defines a third opening  209 , and a second portion of the side wall  203  defines a fourth opening  216 . The stitching element  211  can extend through the first, second, third, and fourth openings  207 ,  208 ,  209  and  216  in a substantially fixed state. The stitching element  211  can hold the front wall  201  and the first portion of the side wall  203  in close engagement with one another so as to form a substantially grease-impermeable seal. Similarly, the stitching element  211  can hold the second portion of the side wall  203  and the back wall  202  in close engagement with one another so as to form a substantially grease-impermeable seal. 
       FIG. 33  depicts another embodiment of a bag  315  that includes a bottom end  325  that is closed via a zipper closure  350 . The bag  315  may resemble (e.g., may be configured similar to and may function similar to) the bags  15 ,  115 , and  215  described above, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “3”. Any suitable feature of the various embodiments of bags  15 ,  115 ,  215  can be incorporated into or otherwise used with the bag  315 , and any suitable feature of the various embodiments of the bag  315  can be incorporated into or otherwise used with the bags  15 ,  115 ,  215 . Further, the bag  315  may be assembled and/or used according to any suitable method, such as any suitable method discussed above with respect to the bags  15 ,  115 ,  215 . 
     With reference to  FIG. 33 , the bottom end  325  of the bag can comprise a zipper closure  350 . As used herein, the terms “top end” and “bottom end” are not absolute and thus should not be construed as limiting. In general, these terms are used from the perspective of a bag manufacturer. Accordingly, in some embodiments, the “bottom end” of a bag may ultimately serve as the “top end” of the bag via which an end user may access the contents of a filled bag. 
     In certain embodiments, the zipper closure  350  can be reclosable such that the closure can be selectively opened or closed repeatedly, as desired. In some embodiments, the zipper closure  350  comprises one or more connection portions  360 , which can comprise a skirt, flaps, or extensions. The connection portions  360  can be connected to the bottom end  325  of the tube body  321  in any suitable manner, and in some embodiments, can form a substantially airtight, fluid-tight, and/or grease-impermeable seal therewith, as further discussed below. The body  321  can resemble any suitable embodiment of the similarly numbered bag bodies  21 ,  121 ,  221  described above. 
     In some embodiments, the zipper closure  350  comprises a first zipper track  372  and a second zipper track  374  that are configured to selectively engage each other and disengage from each other. In some embodiments, the zipper tracks  372 ,  374  can form a substantially airtight, fluid-tight, and/or grease-impermeable seal when engaged with each other. In further embodiments, the zipper closure comprises a sliding block  380  configured to transition the zipper tracks  372 ,  374  between the engaged and disengaged states. The block  380  can move between two stops  382 ,  384 , which can serve to limit the translational movement of the block  380 . 
     With reference to  FIGS. 34 and 35 , in some embodiments, the block  380  can compress the first and second zipper tracks  372 ,  374  into sealed contact with each other to transition the zipper tracks  372 ,  374  to the engaged state. The block  380  can cause the first and second zipper tracks  372 ,  374  to separate from each other to transition the zipper tracks  372 ,  374  to the disengaged state. 
     With reference to  FIG. 35 , in some embodiments, the connection portion  360  of the zipper closure  350  comprises a heat sealable material. In some embodiments, the connection portion  360  is placed in contact with an outer surface of a heat sealable portion of the outer ply  331  (e.g., the film  333 ) and is heat sealed thereto. With reference to  FIG. 35 , in other embodiments, the connection portion  360  is placed in contact with an inner surface of a heat sealable portion of the inner ply  351  (e.g., the film  354 ) and is heat sealed thereto. Any suitable heat sealing methods and materials may be used, such as those discussed herein. 
       FIG. 36  depicts Table 5, which includes comparative measurements of a variety of bags, such as embodiments of bags depicted in  FIGS. 4-12 and 16A-16B  and described in the accompanying text. In particular, various properties are compared among a typical pet food bag (both the bag as a whole and an outer ply thereof), an illustrative, non-limiting embodiment of a composite bag (e.g., a bag comprising a multi-layered construction), a 100% polyolefin bag, and a common woven polypropylene sewn-open-mouth bag. The typical pet food bag represented in the first row of data in Table 5 comprises a construction having a CSR4 outer ply (a bleached 41 pound per 3,000 square feet clay-coated grease-resistant treated paper), two plies of multiwall Kraft, and 2 plies of 0.75 mil BOPP film liner. The second row of data in Table 5 represents measurements related to the CSR4 outer ply of the typical pet food bag (i.e., the pet food bag represented in the first row of data). In particular, the label “Failure-Current” represents a stage at which the outer ply has ripped or torn. In certain of such instances, the entire package can be considered a failure at the “Failure-Current” state, even though remaining plies of the package have not failed, since consumers are less likely to purchase the package due to visible damage to the package. The composite bag represented in the third row of data in Table 5 comprises a 48 gauge PET layer, a 50 pound bleached extensible paper layer, and a 3 mil coextruded film inner ply. The typical woven polypropylene bag represented in the fifth row of data in Table 5 includes a 0.75 mil BOPP extrusion laminated to 850 denier weave having an 8×10 thread count that is coated with 1.0 mil PE; the extrudate is a PP copolymer having a thickness of 1.0 mil. 
     The tests performed on the various bags are listed in the first row of Table 5. It is noted that the abbreviation “MD” is used to denote “Machine Direction,” and the abbreviation “CD” is used to denote “Cross Direction.” For the examples shown, dull probe puncture resistance was measured in accordance with test method ASTM D5748, tear resistance was measured in accordance with test method TAPPI T414, tear initiation was measured in accordance with test method ASTM D1004-07, tensile, elongation was measured in accordance with test method TAPPI T494, and taber stiffness was measured in accordance with test method ASTM D5748. 
     As shown in  FIG. 37 , other tests can be performed to compare embodiments of composite bags, including configurations of bags as depicted in  FIGS. 4-12 and 16A-16B  with other bag varieties. For example, it can be desirable to compare the results of drop tests to determine the relative durability of the composite bag as compared with other bag varieties. One suitable drop test can be performed in accordance with test method ASTM D 5276 and/or test method TAPPI UM 806. The foregoing tests can also be altered or augmented. In some instances, the drop test can comprise a 6-stage cycle, with each stage comprising dropping the bag from a height of 4 feet. The 6 stages of the cycle can comprise separately dropping the bag on its front, back, left edge, right edge, top, and bottom. In some instances, testing can be stopped after three full dropping cycles (i.e., after 18 total drops of the bag). Drop test results can depend on the bag design style (e.g., SOM vs. pinch) and upon the filled weight of the bag. 
     The typical pet food bag represented in the first and third rows of data in Table 6 comprises a construction having a CSR4 outer ply (a bleached 41 pound per 3,000 square feet clay-coated grease-resistant treated paper), two plies of 50 pound multiwall Kraft, and one ply of 1.25 mil BOPP. For the first row of data, the pet food bag is formed with a pinched bottom seal and a pinched top seal; for the third row of data, the pet food bag comprises a sewn-open-mouth configuration. The composite bag represented in the second and fifth rows of data in Table 6 comprises a 48 gauge PET layer, a 50 pound bleached extensible paper layer, and a 3 mil coextruded film inner ply. For the second row of data, the composite bag is formed with a pinched bottom seal and a pinched top seal; for the fifth row of data, the composite bag comprises a sewn-open-mouth configuration. The typical woven polypropylene bag represented in the fourth row of data in Table 6 includes a 0.75 mil BOPP extrusion laminated to 850 denier weave having an 8×10 thread count that is coated with 1.0 mil PE; the extrudate is a PP copolymer having a thickness of 1.0 mil. 
     As shown in Table 6, in some cases, a typical pinch-bottom/pinch-top pet food bag filled with 20 pounds of pet food and subjected to the conditions of a test such as described above can experience more than 18 drops before failing. However, in other cases, a typical pinch-bottom/pinch-top pet food bag can average about 15 drops before reaching a Failure-Current state, which is often the result of gusset failures and outer ply failures. When the pinch-construction pet food bag is filled with 52 pounds of pet food, it can average about 5 drops before failing. 
     The composite bag of the present example, which has a pinch-bottom/pinch-top configuration and is filled with 20 pounds of pet food can experience more than 18 drops before failing. In contrast to the typical pet food bag, the composite bag of the present example generally is not prone to gusset failures or outer ply failures due to its laminated structure and the strength of the materials it contains. When filled with 52 pounds of pet food, the composite bag can average about 7.5 drops before failing. Often, the mode of failure in such instances is a failure of a back seam that runs along the longitudinal length of the bag (e.g., the seam  75 , and related structures disclosed herein). 
     A typical sealed-open-mouth pet food bag subjected to the testing conditions can experience 9.1 drops before failing, and a composite sealed-open-mouth pet food bag subjected to the testing conditions can experience 9.2 drops before failing. 
     Various differences between the specific embodiment of a composite bag used in the tests and each of the other bags are evident from Table 5. For example, as compared with a typical pet food bag that is tested in its entirety (i.e., the first row of data in Table 5), the composite bag used in this particular test is more lightweight, more puncture-resistant, more tear-resistant, slightly less resistant to tear initiation, exhibits greater tensile strength, has a greater capacity to elongate (is “stretchier”), and is less stiff in a machine direction but stiffer in a cross direction. As compared with typical pet food bag that is tested to the “Failure-Current” state described above (i.e., the second row of data in Table 5), the composite bag is significantly more puncture resistant, more tear resistant, and less prone to tearing. Additionally, as is apparent from the drop test results, the composite bag can be considered to have superior overall strength and to hold up better under typical product handling conditions. 
     As shown in Table 6, a typical sewn-open-mouth pet food bag filled with 52 pounds of pet food can fail after only 3 drops. The typical woven polypropylene bag and the composite bag of the present example each can be more durable than the typical pet food bag, each failing after about 9.2 drops on average. In many instances, the woven polypropylene and composite bags fail due to ruptures of the sewing line. 
     The foregoing examples should not be interpreted as limiting. For example, many embodiments of a composite bag can have measurements that are different from those listed in Tables 5 and 6. To illustrate, in various embodiments, a composite bag can have a dull probe puncture resistance within a range of from about 5,000 grams to about 8,000 grams, a machine-direction tear resistance within a range of from about 2,000 grams to about 4,000 grams, a cross-direction tear resistance within a range of from about 3,000 grams to about 6,000 grams, a machine-direction tear initiation within a range of from about 1,000 grams to about 3,000 grams, a cross-direction tear initiation within a range of from about 1,000 grams to about 3,000 grams, a machine-direction tensile strength within a range of from about 30 pounds per inch to about 50 pounds per inch, a machine-direction stretch within a range of from about 3% to about 15%, a cross-direction tensile strength within a range of from about 15 pounds per inch to about 30 pounds per inch, a cross-direction stretch within a range of from about 5% to about 15%, a machine-direction taber stiffness within a range of from about 2.5 to about 5.0, and/or a cross-direction taber stiffness within a range of from about 3.0 to about 7.0. Any subset of the foregoing ranges is possible, and values outside of the listed ranges are also possible. 
     Non-limiting examples compatible with certain embodiments described herein are now provided. The examples are given by way of illustration, and are not intended to limit the disclosure herein. 
     EXAMPLE 1 
     In certain embodiments, a material for forming a bag  15 ,  115 ,  215 , and/or  315  is laminated on an in-line tuber. Specifically, an approximately 48 gauge PET layer (e.g., film  33 ) is reverse printed and laminated to bleached 35 lb. paper (e.g., paper layer  35 ), which in turn is laminated to a 5-layer co-extruded film (e.g., inner ply  51 ) that contains a nylon core (e.g., core layer  55 ). The 35 lb. paper and 5-layer co-extruded film are laminated to each other via solventless adhesive. For material that is used in bags that are configured to contain about 20 or more kilograms of product, the thickness of the co-extruded film is about 4 mils. For material that is used in bags that are configured to contain less than about 20 kilograms of product, the thickness of the co-extruded film is about 3 mils. The multi-layer, laminated material is then converted to bags on standard converting equipment. 
     Bags formed in the foregoing manner can demonstrate excellent grease resistance, odor resistance, and pest resistance. In some embodiments, bags that contain a food product having a fat content of less than 10% by weight exhibit no grease leakage from a sewn closure (e.g., neither through a sealed end of the bag nor through openings in the bag walls through which a stitching element extends) after three months of storage in an environment at about 130 degrees Fahrenheit. The bags can exhibit substantially no odor leaks under the same conditions. 
     In some embodiments, bags that contain a food product having a fat content of less than 10% by weight exhibit no grease leakage from a sewn closure after nine months of storage in an environment at room temperature. The bags can exhibit substantially no odor leaks under the same conditions. 
     In some embodiments, bags that contain a food product having a fat content of at least about 15% by weight exhibit no grease leakage from a sewn closure after 30 days of storage in an environment at about 130 degrees Fahrenheit. 
     EXAMPLE 2 
     In certain embodiments, a material for forming a bag  15 ,  115 ,  215 , and/or  315  is laminated on an in-line tuber. Specifically, an approximately 48 gauge PET layer is reverse printed and laminated to 50 pound bleached extensible paper, which in turn is laminated to a 5-layer co-extruded film that contains a nylon core. The 50 pound paper and 5-layer co-extruded film are laminated to each other via solventless adhesive. For material that is used in bags that are configured to contain about 20 or more kilograms of product, the thickness of the co-extruded film is about 4 mils. For material that is used in bags that are configured to contain less than about 20 kilograms of product (e.g., between about 2 kg and about 10 kg), the thickness of the co-extruded film is about 2 mils. The multi-layer, laminated material is then converted to bags on standard converting equipment. Bags formed in the foregoing manner can demonstrate grease and odor resistance such as that described above with respect to Example 1. 
       FIG. 38  illustrates a perspective view of another embodiment of a bag  415  that comprises a composite material. The bag  415  can resemble the bags  15 ,  115 ,  215 ,  315  described above in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “4”. Any suitable feature of the various embodiments of the bags  15 ,  115 ,  215 ,  315  described above can be incorporated into or otherwise used with the bag  415 , and any suitable feature of the various embodiments of the bag  415  can be incorporated into or otherwise used with the bags  15 ,  115 ,  215 ,  315 . Further, the bag  415  may be assembled and/or used according to methods that may, in certain respects, resemble those discussed above with respect to the bags  15 ,  115 ,  215 ,  315 . For example, any suitable closure arrangement, or combination of closure arrangements, described above may be used with the bag  415 . 
     The bag  415  can comprise a body portion  421  similar to the body portions  21 ,  121 ,  221 ,  321  described above. For example, in some embodiments, the body portion  421  may be formed from one or more materials that are the same as those that form some or all of the body portions  21 ,  121 ,  221 ,  321 . However, in some embodiments, the relative orientations of the various materials (e.g., the ordered layering of the materials) may vary from those of the bags  15 ,  115 ,  215 ,  315 , as further described below. 
     In certain embodiments, the body portion  421  can be substantially tubular in form and may, for example, define a front wall  401 , a back wall  402 , a first side wall  403 , and a second side wall  404 . The bag  415  can define a top end  423 , which is depicted in an open configuration such that a product can be received into the bag  415 , and the product can be maintained within the bag  415  via a closed bottom end  425 . 
     In some embodiments, the body portion  421  comprises a sheet of material that is folded or otherwise formed into the substantially tubular structure. The body portion  421  may comprise a composite material, which can include multiple layers or plies. The term “ply,” as used herein, is a broad term and is not intended to limit the disclosure. For example, the terms “ply” and “layer” may be used synonymously herein, and a given ply may itself include multiple layers or plies. Thus, although certain embodiments described above are cast in terms of inner and outer plies, in some instances, one or more of the inner and outer plies each may include multiple plies or layers. 
     The bottom end  425  is depicted in a closed pinch-bottom configuration. Any other suitable closure configuration may be used, including, for example, any of those depicted in  FIGS. 13-16B  and  FIGS. 25-26  and described in the associated text. Similarly, the bottom end  425  may be formed into a variety of closed configurations via sewing, such as, for example, any of the sewn closures depicted in  FIGS. 29-32B  and described in the associated text. In some embodiments, the top bottom end  425  comprises a resealable closure, such as, for example, any of the zipper closures depicted in  FIGS. 33-35  and described in the associated text. The top end  423  may be closed via any suitable configuration, including any of the configurations described herein with respect to the bottom end  425 . 
       FIG. 39  illustrates an exploded partial perspective view of a body material, or a composite laminate material, from which the bag  415  may be formed. In the illustrated embodiment, the material comprises an outer ply  431 , a paper layer  435 , and an inner ply  451 . The outer ply  431  may comprises a tough extensible film. For example, the outer ply  431  can comprise one or more layers  481  of a polyamide-based film, such as, for example, a nylon film. The layer  481  can comprise any suitable nylon material, such as, for example, the nylon materials described above. In some embodiments, the layer  481  comprises a cast nylon film, such as, for example, a film of nylon 6,6 formed via a cast-film process. In some embodiments, the layer  481  comprises Dartek® cast nylon film, which is available from Exopack of Spartanburg, S.C. In various embodiments, the layer  481  can comprise a nylon film having a thickness of from about 0.5 mil to about 3.0 mil, from about 0.75 mil to about 2.5 mil, from about 1.0 mil to about 2.5 mil, no less than about 0.5 mil, no less than about 0.75 mil, no less than about 1.0 mil, no less than about 1.5 mil, no less than about 2.0 mil, about 0.75 mil, or about 1.0 mil. Other thicknesses are also possible. 
     The paper layer  435  may comprise an extensible paper, such as, for example, any suitable extensible paper described above. In some embodiments, the extensible paper has relatively high tensile energy absorption (TEA) indices in the machine direction and the cross direction. For example, in various embodiments, the machine direction TEA index of the paper layer  435  is within a range of from about 12.0 foot-pounds per square foot to about 20.0 foot-pounds per square foot, is no less than about 12.0 foot-pounds per square foot, no less than about 14.0 foot-pounds per square foot, no less than about 16.0 foot-pounds per square foot, no less than about 18.0 foot-pounds per square foot, or no less than about 20.0 foot-pounds per square foot. In other or further embodiments, the cross direction TEA index of the paper layer  435  is within a range of from about 14.0 foot-pounds per square foot to about 24.0 foot-pounds per square foot, is no less than about 14.0 foot-pounds per square foot, no less than about 16.0 foot-pounds per square foot, no less than about 18.0 foot-pounds per square foot, no less than about 20.0 foot-pounds per square foot, no less than about 22.0 foot-pounds per square foot, or no less than about 24.0 foot-pounds per square foot. In various embodiments, the paper layer  435  can comprise Polar® extensible paper or PolarX extensible paper, which are available from Premium 1 Papers of British Columbia, Canada. In some embodiments, the paper layer  435 , or the extensible properties thereof, can cooperate with and/or reinforce an extensible outer ply  431  so as to increase the strength (e.g., the tear resistance, puncture resistance, etc.) of the bag material. For example, the outer ply  431  and the paper layer  435  can be stretched or otherwise deformed in tandem, and, together, can be more resistant to tearing, puncturing, or otherwise being compromised than if one or the other of the outer ply  431  and the paper layer  435  were inextensible. 
     In other embodiments, the paper layer  435  may comprise a bleached clay coated paper. In still other embodiments, the paper layer  435  may comprise an unbleached Kraft paper. In various embodiments, the paper layer  435  has a basis weight within a range of from about 30 pounds per ream to about 80 lbs per ream, from about 40 pounds per ream to about 70 pounds per ream, no less than about 30 pounds per ream, no less than about 40 pounds per ream, no less than about 50 pounds per ream, no less than about 60 pounds per ream, or can be about 50 pounds per ream. In various embodiments, the paper layer  435  can have a thickness within a range of from about 2.5 mil to about 4.5 mil, about 3.0 to about 4.0 mil, about 3.2 to about 3.7 mil, no less than about 2.5 mil, no less than about 3.0 mil, no less than about 3.2 mil, or no less than about 3.5 mil. 
     In certain embodiments, the paper layer  435  is substantially free of fluorocarbons, such that the paper layer  435  either comprises no fluorocarbons or only trace amounts of fluorocarbons. For example, the paper layer  435  can be included in the laminate material without first being treated with fluorocarbons. Many known bag structures utilize fluorocarbon-treated paper due to the grease-resistant characteristics of such paper. However, certain embodiments of the laminate structures used to form the bags  415  function well without fluorocarbon treated paper due to printing properties and/or grease-resistant properties of their outer ply  431  and/or due to grease-resistant properties of their inner ply  451 , as further discussed below. In other embodiments, fluorocarbon-treated paper may be used. 
     In some embodiments, at least a portion of an outer surface of the paper layer  435  can be surface printed prior to lamination to the outer ply  431 . For example, in some embodiments, the outer ply  431  is substantially clear or transparent such that an outer surface of the paper layer  435  is visible through the outer ply  431 . In certain of such embodiments, it may be desirable for the paper layer  435  and/or the inner ply  451  to be substantially grease resistant so as to prevent grease spots from eventually developing on the paper layer  435 , which would be visible through the outer ply  431 . 
     In other embodiments, at least a portion of the outer ply  431  is reverse printed (e.g., in a manner such as that depicted in  FIG. 5C  with respect to the film  33 ). Any combination of printing on an inner surface of the outer ply  431  and/or printing on an outer surface of the paper layer  435  is possible. In some embodiments, the outer ply  431  is flood-coat printed such that the printing on the outer ply  431  can substantially mask any grease spots that may develop on the paper layer  435 . Accordingly, in certain of such embodiments, the inner ply  451  and/or the paper layer  435  can be permeable to grease substantially without affecting the appearance or grease-resistance of the bag  415 . For example, the outer ply  431  can be substantially grease-resistant as well as flood-coat printed. The flood-coat printing likewise may cover or render imperceptible pin-holing that may result when contents of the bag  415  are sufficiently sharp to develop small openings through the inner ply  451  and the paper layer  435 . Additionally, the outer ply  431  can provide the bag  415  with a plastic and/or shiny appearance. 
     The inner ply  451  may comprise one or more layers  482  of a polyolefin film, such as BOPP. In various embodiments, the layer  482  of BOPP has a thickness within a range of from about 0.5 mil to about 3.5 mil, from about 1.0 mil to about 3.0 mil, no less than about 0.5 mil, no less than about 1.0 mil, no less than about 1.5 mil, no less than about 2.0 mil, no more than about 0.7 mil, or no more than about 1.0 mil. In some embodiments, the layer  482  of BOPP comprises a thickness of about 0.7 mil, and in others, about 2.0 mil. Other materials are also possible, such as those discussed above with respect to the inner ply  51 . 
     In some embodiments, the inner ply  451  comprises a coextruded film, which can, in further embodiments, resemble the coextruded films discussed above. For example, the inner ply  451  can resemble the inner ply  51  illustrated in  FIG. 10A . In certain of such embodiments, the inner ply  451  includes a nylon core sandwiched between two layers of metallocene LDPE. The nylon core can be connected with the metallocene LDPE layers via suitable tie layers. In other embodiments, the inner ply  451  includes a polypropylene core between metallocene LDPE layers. In various embodiments, the thickness of the inner ply  451  is within a range of from about 2.5 mil to about 4.0 mil, no less than about 2.5 mil, no less than about 3.0 mil, no less than about 3.5 mil, or no less than about 4.0 mil. In other or further embodiments, the thickness of each metallocene LDPE layer can be within a range of from about 10 percent to about 25 percent, no less than about 10 percent, no less than about 15 percent, no less than about 20 percent, or no less than about 25 percent of the total thickness of the inner ply  451 . In some embodiments, the core of the coextruded film can provide puncture resistance, toughness, and/or grease resistance. 
     In some embodiments, the inner ply  451  comprises one or more heat-sealable films. For example, in some embodiments, the heat-sealable films can resemble the heat-sealable films described above with respect to the inner ply  51 . In other or further embodiments, the heat-sealable films can comprise metallocene LDPE. The one or more heat-sealable films can allow one or more of the ends  423 ,  425  of the bag  415  to be heat sealed in a manner such as described above. Likewise, the one or more heat-sealable films can be coupled with a resealable closure, such as, for example, the zipper closure  350  described above. 
     In certain embodiments, the inner ply  451  is substantially impermeable to grease and oil. In various embodiments, the inner ply  451  and/or the outer ply  431  can provide grease-resistant properties similar to those of other bags described herein (e.g., the bag  15  depicted in  FIG. 4  and described in the associated text). 
       FIG. 40  illustrates a cross sectional view of the composite material configuration of  FIG. 39  after the layers of material have been laminated to one another. In the illustrated embodiment, the outer ply  431  is adhered to the paper layer  435  via a tie layer  491 . In certain embodiments, the tie layer  491  comprises a layer of solventless adhesive. Any suitable solventless adhesive may be used, such as, for example, one or more of the solventless adhesives described above. In some embodiments, the adhesive comprises a polyurethane-based single-component solventless adhesive, which may be moisture cured. For example, the tie layer  491  can comprise Liofol® Tycel® 7910™, which is available from Henkel Corporation of Rocky Hill, Conn. Other suitable adhesives are available from HB Fuller Company of Vadnais Heights, Minnesota, from Ashland Inc. of Covington, Ky., and from Rohm and Haas Company of Philadelphia, Pa. In other embodiments, the tie layer  491  can comprise a solvent adhesive. In various embodiments, the adhesive can provided in an amount of from about 2.0 pounds to about 3.0 pounds per ream, no less than about 2.0 pounds per ream, no less than about 2.5 pounds per ream, no less than about 3.0 pounds per ream, or about 2.5 pounds per ream. In still other embodiments, the outer ply  431  can be joined to the paper layer  435  via extrusion lamination. 
     In the illustrated embodiment, the inner ply  451  is adhered to the paper layer  435  via a tie layer  492 . In certain embodiments, the tie layer  492  comprises a solventless adhesive. Any suitable solventless adhesive may be used, such as, for example, one or more of the solventless adhesives described above. In other embodiments, the tie layer  492  comprises a solvent adhesive. In still other embodiments, the inner ply  451  can be joined to the paper layer  435  via extrusion lamination. In some embodiments, in-line lamination is used to join the inner ply  451  and the paper layer  435  via a water-based adhesive. Any suitable water-based adhesive may be used. For example, in some embodiments, Product No. 33-4057 from Henkel Corporation of Rocky Hill, Conn. may be used. 
     In various embodiments, a total thickness of the body material of which the body portion  421  is formed can be within a range of from about 4.0 mil to about 11.5 mil, from about 5.0 mil to about 10.0 mil, from about 6.0 mil to about 9.0 mil, can be no less than about 4.0 mil, no less than about 5.0 mil, no less than about 6.0 mil, no less than about 7.0 mil, no less than about 8.0 mil, no less than about 9.0 mil, no less than about 10.0 mil, no more than about 11.0 mil, no more than about 10.0 mil, no more than about 9.0 mil, no more than about 8.0 mil, no more than about 7.0 mil, or no more than about 6.0 mil. In various embodiments, the outer layer  481  can define a thickness that is within a range of from about 10 percent to about 40 percent, from about 15 percent to about 35 percent, is no less than about 10 percent, no less than about 15 percent, no less than about 20 percent, or no less than about 25 percent of the total thickness of the body material. In other or further embodiments, the paper layer 435 can define a thickness that is within a range of from about 20 percent to about 80 percent, from about 30 percent to about 70 percent, from about 40 percent to about 60 percent, is no less than about 20 percent, no less than about 30 percent, no less than about 40 percent, no less than about 50 percent, no less than about 60 percent, or no less than about 70 percent of the total thickness of the body material. In other or further embodiments, the inner layer 451 can define a thickness that is within a range of from about 10 percent to about 50 percent, from about 15 percent to about 40 percent, from about 20 percent to about 30 percent, is no less than about 10 percent, no less than about 15 percent, no less than about 20 percent, no less than about 30 percent, or no less than about 40 percent of the total thickness of the body material. 
       FIG. 41  illustrates a partial perspective view of the material of  FIG. 40 , from which the bag  415  is formed. To aid in identifying the various layers, the outer ply  431  and the paper layer  435  are depicted as being partially peeled back. After the outer ply  431 , the paper layer  435 , and the inner ply  451  have been laminated, the material can be formed into a tubular structure, such as that depiction of  FIGS. 11-12  and described in the associated text. Lateral sides  473  of the material can be arranged in an overlapping fashion, to form a seam, as previously described. 
     One or more hot melt adhesives may be applied to an outer surface of the bag  415  to form a pinch-type closure, such as any of the pinch-type closures previously described. In some embodiments, at least one end of the bag  415  is closed via a pinch closure such as those shown in  FIGS. 13-16B  and described in the associated text. For example, the front wall  401  of the bag  415  can be longer than the rear wall  402  of the bag  415  so as to form a flap that can be folded over the rear wall  402 . A suitable hot melt adhesive may be applied between the flap and the rear wall  402  such that when heat and pressure are applied thereto, the flap and the rear wall  402  are retained in a pinch fold closure configuration. Any suitable hot-melt adhesive may be used. In some embodiments, polyamide hot-melt adhesives are used. For example, in various embodiments, Product Nos. 34-3402 or 34-3412 from Henkel Corporation of Rocky Hill, Conn. may be used. 
     In some embodiments, a portion of the bag to which the hot melt adhesive is to be applied, or with which the hot melt adhesive will otherwise come into contact, is preheated. For example, in some embodiments having a pinch-type closure such as that depicted in  FIGS. 14A and 14B , the front wall  401  can include a flap such as the flap  45  of the front wall  41  discussed above with respect to the bag  15 . In like manner, an inner face of the flap of the front wall  401  and/or a portion of the back wall  402  can be preheated, as discussed above with respect to the bag  15 . 
     The ends of the bag  415  may be closed using any other suitable techniques. For example, in some embodiments, at least one end is closed via stitching, such as that shown in  FIGS. 29-32B  and described in the associated text. 
       FIGS. 42-43  illustrate another embodiment of a bag  515  and a composite laminate material from which the bag  515  may be formed. With reference to  FIG. 42 , a partial perspective view of a lower end  525  of the bag  515  is shown. As illustrated, the lower end  525  can be closed via a compressed lip  571 . The bag  515  may have a configuration that resembles that of the bag  415  and other bags disclosed herein, and may function in similar manners. The configuration of closed end  525  may be said to be a pinch closure. 
       FIG. 43  illustrates a cross sectional view along the view line  43 - 43  shown in  FIG. 42 , which shows the composite laminate structure of the bag  515  and the configuration of the compressed lip  571 . The bag  515  may comprise an outer ply  531  of nylon and a paper layer  535 , which can resemble the outer ply  431  and the paper layer  435 , respectively, described above. The bag  515  can include an inner ply  554  that comprises a heat-sealable film, as described herein. The outer ply  531 , the paper layer  535 , and the inner ply  554  may be coupled, respectively, via tie layers  591 ,  592  that may be configured as the tie layers  491 ,  492  described above. 
     The compressed lip  571  may be formed by positioning the heat-sealable films of opposing inner plies  554  adjacent each other and applying heat and pressure, such that a heat seal  550  is formed. Other pinch type closures may be employed with the composite laminate structure of the bag  515 , such as, for example, those depicted in  FIGS. 13-16B  and described in the associated text. In further embodiments, the bag  515  may comprise a zipper closure, such as, for example, those depicted in  FIGS. 33-35  and described in the associated text. 
       FIG. 44  illustrates a cross-sectional view of an embodiment of a composite laminate structure that may be employed to form a bag  615 , which can comprise any suitable configuration disclosed herein. The cross-sectional view of  FIG. 44  is similar to the view of  FIG. 40 , and the composite laminate structure of the bag  615  can resemble the structures of the bags  415  and  515  in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “6”. For example, the laminate structure can include an inner ply  651 , a paper layer  635 , a tie layer  691 , and a tie layer  692  that resemble similarly named and numbered features described above, such that the applicable disclosure relative to these features apply equally to the present disclosure. The laminate structure can further include an outer ply  631  that includes both a polyolefin layer  633  and a polyamide layer  681 . The polyolefin layer  633  can overlie the polyamide layer  681 , and can resemble the polyolefin layer  33  described above. For example, in some embodiments, the polyolefin layer  633  can comprise PET, and may be reverse printed. The polyolefin layer  633  can be attached to the polyamide layer  681  via any suitable tie layer  693 . 
       FIGS. 45 and 46  depict another embodiment of a bag  715 , which can comprise any suitable configuration disclosed herein.  FIG. 45  illustrates a cross-sectional view of an embodiment of a composite laminate structure that may be employed to form the bag  715 . The cross sectional view of  FIG. 45  is similar to the view of  FIG. 40 , and the composite laminate structure of the bag  715  can resemble the structures of the bags  415 ,  515 , and  615  in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “7”. For example, the laminate structure can include an inner ply  751 , a first paper layer  735 , an outer ply  731 , a tie layer  791 , and a tie layer  792  that resemble similarly named and numbered features described above, such that the applicable disclosure relative to these features apply equally to the present disclosure. As a further example, the composite laminate structure of bag  715  may be configured to be compatible with the bag end closures described herein, including pinch-type and sewn configurations. In some embodiments, the bag  715  may comprise a zipper closure such as is depicted herein by  FIGS. 33-35  and described in the associated text. 
     In certain embodiments, the bag  715  can include a second paper layer  736 , which can comprise any suitable paper layer described herein. In some embodiments, the paper layers  735 ,  736  are substantially the same as each other. In other embodiments, the paper layers  735 ,  736  can differ from each other, such as, for example, in basis weight and/or paper type. In some embodiments, the first paper layer  735  includes an extensible paper and the second layer  736  includes a Kraft paper. The paper layers  735 ,  736  can be joined to each other in any suitable fashion. In some embodiments, the paper layers  735 ,  736  are adhered to each other over all or substantially all of an area over which the paper layers  735 ,  736  face each other via any suitable adhesive  794 . In other embodiments, spot pasting may be employed to attach the paper layers  735 ,  736  to each other. 
     In various embodiments, a total thickness of the body material can be within a range of from about 5.0 mil to about 15.0 mil, from about 5.0 mil to about 12.0 mil, from about 6.0 mil to about 10.0 mil, can be no less than about 5.0 mil, no less than about 6.0 mil, no less than about 7.0 mil, no less than about 8.0 mil, no less than about 9.0 mil, no less than about 10.0 mil, or no less than about 11.0 mil. In various embodiments, the outer ply  731  can define a thickness that is within a range of from about 5 percent to about 35 percent, from about 10 percent to about 30 percent, is no less than about 5 percent, no less than about 10 percent, no less than about 15 percent, no less than about 20 percent, or no less than about 25 percent of the total thickness of the body material. In other or further embodiments, the first paper layer  735  can define a thickness that is within a range of from about 15 percent to about 70 percent, from about 25 percent to about 60 percent, from about 30 percent to about 50 percent, is no less than about 15 percent, no less than about 25 percent, no less than about 30 percent, no less than about 40 percent, no less than about 50 percent, or no less than about 60 percent of the total thickness of the body material. In other or further embodiments, the second paper layer  736  can define a thickness that is within a range of from about 15 percent to about 70 percent, from about 25 percent to about 60 percent, from about 30 percent to about 50 percent, is no less than about 15 percent, no less than about 25 percent, no less than about 30 percent, no less than about 40 percent, no less than about 50 percent, or no less than about 60 percent of the total thickness of the body material. In other or further embodiments, the inner ply  751  can define a thickness that is within a range of from about 5 percent to about 40 percent, from about 10 percent to about 35 percent, from about 15 percent to about 30 percent, is no less than about 5 percent, no less than about 10 percent, no less than about 15 percent, no less than about 20 percent, no less than about 25 percent, or no less than about 30 percent of the total thickness of the body material. 
       FIG. 46  depicts a compressed lip configuration  771  of a pinch-type closure similar to those depicted in  FIGS. 13-16B  and described in the associated text. The composite laminate structure of the material from which the bag  715  is formed may be compatible with other types of bag end closures disclosed herein. The outer ply  731 , the paper layer  735 , second paper layer  736 , and inner ply  751  form a bag wall. As described above, an end of a bag can be closed by bringing two portions of the bag wall adjacent to each other and fixedly coupling them together. In the embodiment depicted in  FIG. 46 , one of the portions of the bag wall (e.g., a rear wall portion) is longer than an opposing portion of the wall (e.g., a front wall portion) such that the longer portion can wrap around and overlie the shorter wall portion. An adhesive layer  764  can fixedly couple the two portions of the bag wall to each other. The adhesive layer  764  can comprise any suitable adhesive, such as, for example, a hot melt adhesive. The hot melt adhesive can comprise, for example, any suitable hot melt adhesive described above with respect to the adhesive  64 . In some embodiments, a portion of the bag  715  to which the hot melt adhesive  764  is to be applied is preheated, such as described above with respect to the bag  415 . In certain embodiments, a seal  750  may be formed in addition to that provided by the adhesive layer  764 , which can fixedly couple the bag walls together. The seal  750  may comprise a heat seal, if inner ply  751  comprises a heat-sealable film. Otherwise, if present, the seal  750  may comprise a tie layer as disclosed herein. 
       FIGS. 47 and 48  depict another embodiment of a bag  815 , which can comprise any suitable configuration disclosed herein.  FIG. 47  illustrates a cross-sectional view, similar to that of  FIG. 40 , of an embodiment of a composite laminate structure that may be employed to form the bag  815 . The composite laminate structure of the bag  815  can resemble the structures of the bags  415 ,  515 ,  615 ,  715  in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “8”. For example, the laminate structure can include an outer ply  931 , a first paper layer  935 , a second paper layer  936 , and an inner ply  951  that resemble similarly named and numbered features described above, such that the applicable disclosure relative to these features apply equally to the present disclosure. Likewise, the laminate structure can include tie layers  991 ,  992 , and the paper layers  935 ,  936  can be joined via an adhesive  994 . The outer ply  931  can include an outermost polyolefin layer  933 , which can be reverse printed in some embodiments. The polyolefin layer  933  can be attached to a 
     In the illustrated embodiment, a portion of the outer ply  831  and the tie layer  891  immediately underlying the outer ply  831  include one or more channels  832  extending through them so as to provide access to the first paper layer  835 . The channels  832  can be formed in any suitable manner, such as via perforations, slits, or other mechanical alterations. 
     As shown in  FIG. 48 , at least one end of the bag  815  can be closed via a compressed lip configuration  871  of a pinch-type closure, similar to those depicted in  FIGS. 13-16B . In a manner such as previously described, an end of a bag  815  can be closed by bringing two bag walls into close proximity and fixedly coupling them together. In the embodiment illustrated in  FIG. 48 , one of the bag walls is longer than the other (e.g., includes a flap) such that the longer portion can wrap around and overlie the shorter bag wall to form a seal therewith via an adhesive layer  864 . In other or further embodiments, a seal  850  may be formed in addition to that provided by the adhesive layer  864 , which can fixedly couple the bag walls together. The seal  850  may comprise a heat seal, if inner ply  851  comprises a heat-sealable film. Otherwise, if present, the seal  850  may comprise a tie layer as disclosed herein. 
     The channels  832  may be located at or near an end of the bag  815 . In the illustrated embodiment, the channels  832  are primarily located on the shorter bag wall portion such that a seal between the outer ply  831  of the shorter portion and the inner ply  851  of the longer portion is enhanced. For example, the adhesive layer  864  may form a stronger bond with the paper layer  835  than it does with the outer ply  831 . In certain embodiments, the adhesive layer  864  comprises a hot melt adhesive, such as, for example, any suitable hot melt adhesive disclosed herein. 
       FIG. 49  depicts a cross-sectional view, similar to that of  FIG. 40 , of another embodiment of a composite laminate structure that may be employed to form a bag  915 , which can comprise any suitable configuration disclosed herein. The composite laminate structure of the bag  915  can resemble the structures of the bags  415 ,  515 ,  615 ,  715 ,  815  in many respects, thus like features are identified with like reference numerals, with a leading hundreds numeral incremented to the value “9”. For example, the laminate structure can include an outer ply  931 , a first paper layer  935 , a second paper layer  936 , and an inner ply  951  that resemble similarly named and numbered features described above, such that the applicable disclosure relative to these features apply equally to the present disclosure. Likewise, the laminate structure can include tie layers  991 ,  992 , and the paper layers  935 ,  936  can be joined via an adhesive  994 . 
     The outer ply  931  can include both a polyolefin layer  933  and a polyamide layer  981 . The polyolefin layer  933  can overlie the polyamide layer  981 , and can resemble the polyolefin layers  33 ,  633  described above. For example, in some embodiments, the polyolefin layer  933  can comprise PET, and may be reverse printed. The polyolefin layer  933  can be attached to the polyamide layer  981  via any suitable tie layer  993 . 
     Any suitable feature of the various embodiments of the bags  15 ,  115 ,  215 ,  315 ,  415 ,  515 ,  615 ,  715 ,  815 ,  915  described above can be incorporated into or otherwise used with any of the remaining bags  15 ,  115 ,  215 ,  315 ,  415 ,  515 ,  615 ,  715 ,  815 ,  915 . Further, the bags  15 ,  115 ,  215 ,  315 ,  415 ,  515 ,  615 ,  715 ,  815 ,  915  may be assembled and/or used according to methods that may, in certain respects, resemble those discussed above with respect to any of the remaining bags  15 ,  115 ,  215 ,  315 ,  415 ,  515 ,  615 ,  715 ,  815 ,  915 . For example, any suitable body material structure and/or any suitable closure arrangement, or combination of closure arrangements, may be used with a given bag. By way of further illustration, in some embodiments, channels such as the channels  832  of the bag  815  can be provided in a closure region of the bags  615 ,  715 ,  915 . For the bags  615 ,  915 , the channels  832  can extend through the layers  633 ,  681  and  933 , 981  to provide access to the paper layers  635 ,  935 , respectively. 
     Following are non-limiting examples compatible with certain embodiments described herein. The examples are provided by way of illustration, and are not intended to limit the disclosure. 
     EXAMPLE 3 
     Material for forming a bag, such as the material used to form the bag  415 , was laminated on an in-line tuber. The material included an outer ply of 75 gauge Dartek® cast nylon film. The nylon film was laminated to a layer of 50 pound PolarX extensible paper via a polyurethane single-component solventless adhesive—specifically, Henkel Corporation&#39;s Tycel® 7910™ adhesive in an amount of 2.5 pounds per ream. A 2.0 mil layer of BOPP film was then laminated to an opposite side of the extensible paper via Tycel® 7910™ adhesive in an amount of 2.5 pounds per ream. The material was then formed into a pinched bottom open mouth (PBOM) configuration using standard forming equipment and subsequently filled with 35 pounds of dog food. The other open end of the bag was then closed using a pinch closure, such that the top and bottom ends were sealed in a hot-melt-sealed configuration such as that shown in  FIG. 14B . 
     EXAMPLE 4 
     Material for forming a bag, such as the material used to form the bag  715 , was laminated on an in-line tuber. The material included an outer ply of 75 gauge Dartek® cast nylon film. The nylon film was laminated to a layer of 50 pound PolarX extensible paper via a polyurethane single-component solventless adhesive—specifically, Henkel Corporation&#39;s Tycel® 7910™ adhesive in an amount of 2.5 pounds per ream. The extensible paper was then spot-pasted to 40 pound converting Kraft paper, which had a thickness within a range of from 3 mil to 4 mil. Water-based adhesive was used for the spot-pasting. A 70 gage film of BOPP was then laminated to the 40 pound Kraft paper using a water-based adhesive. The material was then formed into a pinched bottom open mouth (PBOM) configuration using standard forming equipment and subsequently filled with 35 pounds of dog food. The other open end of the bag was then closed using a pinch closure, such that the top and bottom ends were sealed in a hot-melt-sealed configuration such as that shown in  FIG. 14B . 
     Bags formed in accordance with Examples 3 and 4 demonstrate excellent performance in a variety of standardized and reproducible tests. For example, the bags can more durable than standard multiwall pet food bags and other bags with composite structures, in that they can be more resistant to puncturing and/or tearing under conditions that may arise during handling of the bags. The tables that follow demonstrate the results of certain tests involving these bags and comparative bags. 
     Drop tests can demonstrate the relative durability of the composite bag structures associated with Examples 3 and 4, as compared with other bag varieties. One suitable drop test can be performed in accordance with test method ASTM D 5276 and/or test method TAPPI UM 806. The foregoing test methods can also be altered or augmented. In some instances, the drop test can comprise a 6-stage cycle, with each stage comprising dropping the bag from a height of 4 feet. The 6 stages of the cycle can comprise separately dropping the bag on its front, back, left edge, right edge, top, and bottom. In some instances, testing can be stopped after three full dropping cycles (i.e., after 18 total drops of the bag). The results of one drop test are set forth in Table 7. 
     
       
         
           
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                 Bag Type 
                 Number of Drops Before Failure 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Multiwall 
                 8 
               
               
                   
                 Composite 
                 10.6 
               
               
                   
                 Example 3 
                 13 
               
               
                   
                 Example 4 
                 18 
               
               
                   
               
            
           
         
       
     
     In Table 7, the “Multiwall” bags consisted of 41 a standard body material having an outer layer of 41 pound bleached clay coated paper. The clay coated paper was spot pasted to an inner ply of 40 pound Kraft, which was spot pasted to another ply of 40 pound Kraft. The inner Kraft ply was laminated to a 70 gauge BOPP film via water-based adhesive. The bag was filled with 35 pounds of dog food and both ends were sealed with a hot-melt pinch closure. The “Composite” bags consisted of an outer layer of 0.48 mil thick PET film laminated via solventless adhesive to a bleached clay-coated paper, and an inner surface of the clay-coated paper was laminated via solventless adhesive to a 2.5 mil thick coextruded film having a nylon core. The “Example 3” and “Example 4” bags were formed in accordance with the descriptions set forth above under the headings “Example 3” and “Example 4,” respectively. The averaged results set forth in Table 7 indicate that the “Example 3” and “Example 4” varieties of bags demonstrated better durability than standard multiwall bags in row one or the specific variety of composite bag in row two. Moreover, the “Example 4” bags were more durable than the “Example 3” bags. 
     Additional tests performed on the varieties of bags used in the drop tests. These additional tests are listed in the header row of Table 8. It is noted that the abbreviation “MD” is used to denote “Machine Direction,” and the abbreviation “CD” is used to denote “Cross Direction.” For the examples shown, sharp probe and dull probe puncture resistances were measured in accordance with test method ASTM D5748, tear resistance was measured in accordance with test method ASTM D1922, and tear initiation was measured in accordance with test method ASTM D1004. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Sharp Probe 
                 Dull Probe 
                 MD 
                 CD 
                 MD 
                 CD 
               
               
                   
                 Puncture 
                 Puncture 
                 Tear 
                 Tear 
                 Tear 
                 Tear 
               
               
                   
                 Resistance 
                 Resistance 
                 Resistance 
                 Resistance 
                 Initiation 
                 Initiation 
               
               
                 Bag Type 
                 (g) 
                 (g) 
                 (g) 
                 (g) 
                 (g) 
                 (g) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Multiwall 
                 N/A 
                 1519 
                 56 
                 55 
                 707 
                 597 
               
               
                 Composite - 
                 1230 
                 6929 
                 385 
                 431 
                 2292 
                 2052 
               
               
                 PET 
               
               
                 Example 3 
                 1051 
                 9500 
                 182 
                 184 
                 2300 
                 2200 
               
               
                 (Composite - 
               
               
                 Nylon) 
               
               
                 Example 4 
                  700 
                 4663 
                 165 
                 138 
                 1119 
                 1029 
               
               
                 Non-woven 
                 1779 
                 16085 
                 1159 
                 1294 
                 4077 
                 3751 
               
               
                   
               
            
           
         
       
     
     In Table 8, the “Multiwall” bag included a structure such as that described above with respect to the “Multiwall” bag of Table 7. The material identified as “Composite—PET” included an outer ply of 48 gauge PET, which was laminated to a layer of 50 pound PolarX extensible paper via a polyurethane single-component solventless adhesive—specifically, Henkel Corporation&#39;s Tycel® 7910™ adhesive in an amount of 2.5 pounds per ream. A 4.0 mil layer of coextruded film having a nylon core was then laminated to an opposite side of the extensible paper via Tycel® 7910™ adhesive in an amount of 2.5 pounds per ream. The material was then formed into a pinched bottom open mouth (PBOM) configuration using standard forming equipment and subsequently filled with 35 pounds of dog food. The other open end of the bag was then closed using a pinch closure, such that the top and bottom ends were sealed in a hot-melt-sealed configuration such as that shown in  FIG. 14B  The “Non-woven” bags consisted of an outermost layer of 0.48 mil thick PET laminated via solventless adhesive to a non-woven fabric comprising PET coated with LDPE and having a weight of 2.5 ounces per square yard, and an inner layer of the non-woven fabric was laminated via solventless adhesive to BOPP film having a thickness of 2.0 mil. The bag was filled and closed in a manner such as that described with respect to the “Composite—PET” bag. 
     As illustrated in Table 8, in various embodiments, bag types formed with composite structures such as those of the bags  415 ,  615 ,  715 ,  815 , and  915  can have improved strength and durability. However, the specific measurements set forth in Table 8 should not be construed as limiting. For example, in various embodiments, a composite bag (e.g., a bag  415 ,  615 ,  715 ,  815 , or  915 , as described above) can have a sharp probe puncture resistance that is within a range of from about 800 grams to about 2,500 grams, from about 1,000 grams to about 2,000 grams, from about 1,000 grams to about 1,500 grams, from about 1,250 grams to about 1,750 grams, is no less than about 800 grams, no less than about 1,000 grams, no less than about 1,250 grams, no less than about 1,500 grams, no less than about 1,750 grams, no less than about 2,000, no less than about 2,250 grams, or no less than about 2,500 grams. In other or further embodiments, the composite bag can have a dull probe puncture resistance that is within a range of from about 4,000 grams to about 8,000 grams, from about 5,000 grams to about 8,000 grams, from about 6,000 grams to about 7,000 grams, is no less than about 4,000 grams, no less than about 5,000 grams, no less than about 6,000 grams, no less than about 7,000 grams, or no less than about 8,000 grams. In other or further embodiments, the composite bag can have a machine-direction tear resistance that is within a range of from about 2,000 grams to about 4,000 grams, from about 2,500 grams to about 3,500 grams, or from about 3,000 grams to about 4,000 grams, is no less than about 2,000 grams, no less than about 2,500 grams, no less than about 3,000 grams, no less than about 3,500 grams, or no less than about 4,000 grams. In other or further embodiments, the composite bag can have a cross-direction tear resistance that is within a range of from about 3,000 grams to about 6,000 grams or from about 4,000 grams to about 5,000 grams, is no less than about 3,000 grams, is no less than about 3,500 grams, is no less than about 4,000 grams, is no less than about 5,000 grams, is no less than about 5,500 grams, or is no less than about 6,000 grams. In other or further embodiments, the composite bag can have a machine-direction tear initiation that is within a range of from about 1,000 grams to about 3,000 grams or from about 1,500 grams to about 2,500 grams, is no less than about 1,000 grams, no less than about 1,500 grams, no less than about 2,000 grams, no less than about 2,500 grams, or no less than about 3,000 grams. In other or further embodiments, the composite bag can have a cross-direction tear initiation that is within a range of from about 1,000 grams to about 3,000 grams or from about 1,500 grams to about 2,500 grams, is no less than about 1,000 grams, no less than about 1,500 grams, no less than about 2,000 grams, no less than about 2,500 grams, or no less than about 3,000 grams. 
     In various embodiments, a composite bag can have a Mullen greater than 100 psi. In other or further embodiments, a composite bag can have a machine-direction tensile strength that is within a range of from about 30 pounds per inch to about 70 pounds per inch, is no less than about 30 pounds per inch, no less than about 40 pounds per inch, no less than about 50 pounds per inch, or no less than about 60 pounds per inch. In other or further embodiments, a composite bag can have a machine-direction stretch that is within a range of from about 3% to about 15%, is no less than about 3%, no less than about 5%, no less than about 10%, or no less than about 15%. In other or further embodiments, a composite bag can have a cross-direction tensile strength that is within a range of from about 15 pounds per inch to about 30 pounds per inch, is no less than about 15 pounds per inch, no less than about 20 pounds per inch, or no less than about 25 pounds per inch. In other or further embodiments, a composite bag can have a cross-direction stretch that is within a range of from about 5% to about 15%, is no less than about 5%, no less than about 10%, or no less than about 15%. In other or further embodiments, a composite bag can have a machine-direction taber stiffness that is within a range of from about 2.5 to about 5.0, is no less than about 2.5, no less than about 3.0, no less than about 4.0, or no less than about 4.5. In other or further embodiments, a composite bag can have a cross-direction taber stiffness that is within a range of from about 3.0 to about 7.0, is no less than about 3.0, no less than about 4.0, no less than about 5.0, or no less than about 6.0. Any subset of the foregoing ranges is possible, and values outside of the listed ranges are also possible. Additionally, it is noted that values recited in this paragraph for Mullen are determined in accordance with test method TAPPI T403, those for tensile and stretch are determined in accordance with test method TAPPI T494, and those for taber stiffness are determined in accordance with test method ASTM D5748. 
     Other ranges may be possible for constructions that include a non-woven layer of material. For example in some embodiments, a bag having a non-woven layer and a construction such as that described above with respect to Table 8 can have a sharp probe puncture resistance within a range of from about 1,000 grams to about 2,800 grams, or that is no less than about 1,000 grams, no less than about 1,500 grams, no less than about 2,000 grams, no less than about 2,500 grams, or no less than about 2,800 grams. 
     In various embodiments, the body material of a composite bag can be configured so as to have stiffness, dead-fold, and/or other handling properties similar to those of standard multiwall Kraft bags. For example, in some embodiments, although only one or two layers of paper may be present in the body material, the body material may be as stiff as constructions having more paper layers. Moreover, the body material may be able to maintain a crease in a fashion similar to standard multiwall Kraft bags. Accordingly, in some embodiments, the body material can behave similarly to standard paper structures, and thus bags can be formed on standard forming equipment with relatively few or even no modifications to the equipment. 
     As a further illustration of the durability of the structures described with respect to the bags  415 ,  515 ,  615 ,  715 ,  815 ,  915 , a fork lift puncture test was devised to test the performance of a bag under abusive handling conditions. In this test, a prong tip comparable to the tips of prongs used in industrial forklifts (in particular, Hyster forklifts) was used. The elongated prong tip weighed 18 pounds and included a sharpened end. The prong tip was dropped from a height of twelve inches above an upward-facing surface of a bag lying on a rigid surface. Thus, the sharpened end of the prong tip fell through twelve inches to impact the upward-facing surface of the bag. The bags can be evaluated on a pass/fail basis, and the severity of the puncture can be noted with respect to the number of plies punctured. Three of the same bag types tested with respect to Table 8 were subjected to the fork lift puncture test, and the results are shown below in Table 9. 
     
       
         
           
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                 Bag Type 
                 Pass/Fail 
                 Severity of Puncture 
               
               
                   
               
             
            
               
                 Multiwall 
                 Fail 
                 Large split 
               
               
                 Example 3 
                 Pass 
                 No puncture-dent formed 
               
               
                 Non-woven 
                 Pass 
                 No puncture-dent formed 
               
               
                   
               
            
           
         
       
     
     Table 10, which is set forth below, presents results from an insect infestation study performed using bags having four different construction types. The various constructions included three different body material configurations and two different end closure configurations. Ten total bags of each construction type were used—five included pet food with a first fat content and another five included pet food with a second fat content. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                   
                   
                   
                 Total Number of Indian Meal 
               
               
                   
                   
                   
                 Moths Observed 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Bag Construction 
                 Bag # 
                 8% Fat 
                 12% Fat 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 CC/MWK/BOPP 
                 1 
                 11 
                 3 
               
               
                   
                 PBOM 
                 2 
                 0 
                 0 
               
               
                   
                   
                 3 
                 0 
                 0 
               
               
                   
                   
                 4 
                 8 
                 0 
               
               
                   
                   
                 5 
                 23 
                 5 
               
               
                   
                 Composite 
                 1 
                 0 
                 0 
               
               
                   
                 PBOM 
                 2 
                 0 
                 0 
               
               
                   
                   
                 3 
                 0 
                 0 
               
               
                   
                   
                 4 
                 0 
                 0 
               
               
                   
                   
                 5 
                 2 
                 0 
               
               
                   
                 Woven Poly/BOPP 
                 1 
                 34 
                 5 
               
               
                   
                 SOM 
                 2 
                 22 
                 4 
               
               
                   
                   
                 3 
                 19 
                 14 
               
               
                   
                   
                 4 
                 3 
                 13 
               
               
                   
                   
                 5 
                 54 
                 7 
               
               
                   
                 Composite 
                 1 
                 12 
                 3 
               
               
                   
                 SOM 
                 2 
                 44 
                 5 
               
               
                   
                   
                 3 
                 15 
                 12 
               
               
                   
                   
                 4 
                 7 
                 0 
               
               
                   
                   
                 5 
                 23 
                 8 
               
               
                   
               
            
           
         
       
     
     In Table 10, the term “PBOM” represents a pinch-bottom-open-mouth configuration and the term “SOM” represents a sewn-open-mouth configuration. For each configuration, the top end of the bag was closed in the same manner as the bottom end of the bag. Thus, for the PBOM configurations, both the top and bottom ends included a pinch-type closure in which a flap extending from one side of the bag was folded over the other side of the bag and adhered thereto with a hot melt adhesive, similar to the closure depicted in  FIG. 14B . For the SOM configurations, both the top and bottom ends included a closures similar to those depicted in  FIG. 30 . 
     For the first set of rows, the term “CC/MWK/BOPP” represents a standard body material having an outer layer of 41 pound bleached clay coated paper available under the name CSR4 from FraserPapers of Toronto, Ontario. The body material further includes two inner plies of 50 pound multiwall kraft. The innermost kraft ply is coated with a 0.7 mil layer of BOPP. The ends of the bag were closed using a polyethylene-based hot melt 
     The results in the second set of rows can be compared with those of the first set of rows. In the second set of rows, the term “Composite” represents a body material having a construction such as that shown in  FIG. 10A . In particular, the body material included an outer ply  31  having an outermost layer  33  of 0.48 mil polyethylene adhered to a paper layer  35  of 50 pound PolarX extensible paper. An inner ply  51  included a 2.5 mil coextruded film having a nylon core  55  with metallocene LDPE layers  53 ,  54  attached to either side thereof via tie layers  37 . The ends of the bag were closed using a polyamide hot melt having Product No. 34-3412, which is available from Henkel Corporation of Rocky Hill, Conn. 
     For the third set of rows, the term “Woven Poly/BOPP” represents a standard body material having an inner layer of 850 denier woven polypropylene fabric having an 8×8 thread count. The body material further included an outer ply of BOPP having a thickness of 0.7 mil. 
     The results in the fourth set of rows can be compared with those of the third set of rows. In the fourth set of rows, the term “Composite” represents a body material such as that described above with respect to the second set of rows. 
     Pet food containing 8% fat by weight was enclosed in five of each variety of bag. Likewise, pet food containing 12% fat by weight was enclosed in five of each variety of bag. The filled bags were randomly placed in a walk-in environmental chamber. The chamber was maintained at 27 degrees C. and 60% relative humidity with a alternating light/dark cycle of twelve hours each. The walk-in chamber included an initial population of 2,000 mixed-sex adult Indian Meal Moths (IMM) ( Plodia interpunctella ). The bags were left inside the chamber for eight weeks. It is noted that the development time for the IMM from egg to adult is 28 days, and that the female IMM, under laboratory conditions, lays  300  eggs at a time. Thus, the bags used in this study were exposed to several generations of IMM. 
     The results reported in Table 10 represent the number of IMM found inside a particular bag. It is believed that an impregnated female IMM would deposit her eggs on a bag at the point where the odor trail of pet food was strongest. The eggs would hatch, and if the odor trail led to a hole which granted access to the interior of the bag, the larva would crawl inside the bag. Once inside the bag, it would feed. If other larvae matured inside the bag and nature took its course, the mature IMM, now inside the bag, would reproduce. As the adult IMM is significantly larger than the larva, it was thought to be extremely difficult for the adult to have access to the inside of the bag directly, absent manufacturing defects in the bag. 
     The results of the experiment indicate that the pet food that included 8% fat had a stronger odor than the pet food that included 12% fat. In general, PBOM closures are more successful at resisting IMM infestation than are SOM closures. For either closure type, however, the Composite construction had a lower rate of IMM infestation. Moreover, the PBOM Composite construction was the most resistant to IMM infestation, and for pet foot having 12% fat, was completely effective at preventing IMM infestation under the experimental conditions set forth above. 
     Any methods disclosed herein comprise one or more steps or actions for performing the described method. The method steps and/or actions may be interchanged with one another. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order and/or use of specific steps and/or actions may be modified. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or “the embodiment” means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, the quoted phrases, or variations thereof, as recited throughout this specification are not necessarily all referring to the same embodiment. 
     Similarly, it should be appreciated that in the above description of embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure. This method of disclosure, however, is not to be interpreted as reflecting an intention that any claim require more features than those expressly recited in that claim. Rather, as the following claims reflect, inventive aspects lie in a combination of fewer than all features of any single foregoing disclosed embodiment. 
     The claims that follow are hereby expressly incorporated into the present written disclosure, with each claim standing on its own as a separate embodiment. Likewise, this disclosure includes all permutations of the independent claims with their dependent claims. For example, additional embodiments capable of derivation from each set of independent and dependent claims are expressly incorporated into the present written description. These additional embodiments can determined by replacing the dependency of all dependent claims with the phrase “any of the preceding claims up to and including the nearest independent claim.” 
     Recitation in the claims of the term “first” with respect to a feature or element does not necessarily imply the existence of a second or additional such feature or element. Recitation in the claims of the term “outer” with respect to an element does not necessarily imply that the element is the outermost of such elements. Similarly, recitation in the claims of the term “inner” with respect to an element does not necessarily imply that the element is the innermost of such elements. Elements recited in means-plus-function format are intended to be construed in accordance with 35 U.S.C. §112 ¶6. It will be apparent to those having skill in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. Embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.