Abstract:
A portable soft sided insulated container has an impermeable liner that provides a liquid holding barrier. The liner is folded from a single monolithic plastic sheet to reduce or eliminate the need for heat welded seams. The liner seats within the container and has a releasable attachment around its lip for mating with the rim of the container. The container has an insulated lid so that the entire assembly may be closed. The liner can be removed for cleaning, or replacement if punctured. When not in use the entire assembly can be folded into a collapsed position for storage.

Description:
This application is a continuation of U.S. patent application Ser. No. 09/199,287 filed Nov. 25. 1998 and issued to U.S. patent No. 6,238,091 on May 29, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to the field of soft sided insulated containers. In particular it relates to soft sided insulated containers having removable impermeable liners for discouraging or preventing the leakage of liquids. 
     In recent times soft sided insulated containers have become popular for carrying either articles that may best be served cool, such as beverages or salads, or warm, such as appetizers, hot dogs, and so on. Such containers are frequently used to carry liquids, whether hot liquids, such as soup containers, coffee or tea, or cold liquids such as beer pop, juices and milk. The containers are typically made in a generally cube like shape, whether of sides of equal length or not, having a base, four upstanding walls, and a top. The top is generally a lid which opens to permit articles to be placed in, or retrieved from, the container. 
     By the nature of their use, it is advantageous for the containers to be water tight. That is, whether to hold melted run-off from ice cubes or to hold spilled liquids, the container must be sufficiently liquid tight that it does not leave a trail of drips, or become moist or sticky to the touch of a person carrying the container. 
     The present inventor has found it disadvantageous to try to seal the container itself. The type of insulating wall used by the present inventor is generally sewn at its seams. Sewn seams have a tendency to leak at the stitches. Another approach is to fold the insulated blanket from which the container is made, to present an assembly that, through folding, has no seams. This is also disadvantageous, in the present inventor&#39;s view, because the insulated blanket used to form the container walls is relatively thick. The thick material does not fold well, in the inventor&#39;s view. It would be preferable to form an impermeable layer that has a relatively thin wall thickness so that the resulting product does not look bulky and cumbersome. 
     It is also advantageous to be able to clean the inside of the insulated container. Spilt liquids may not always have the most attractive air when allowed to dry, and may cause the inside of the container to become unsightly. It is possible to provide a plastic liner for soft sided insulated containers. A see through plastic liner can be made of the minimum amount of material by using only a single layer, and forming seams where the edges of the material meet. A common method of forming such a seam is to weld two adjacent edges together by heating. However, an existing liner of this type is known to have had a tendency for the heat welded seams to develop leaks over time. It would be advantageous to reduce or eliminate the number of heat welded seams formed in areas of the liner that may need to be water tight. 
     In general, manufacture of an assembly of this type emphasizes cost reduction. One common source of cost savings is a reduction of the raw material used. However, the present inventor has observed, counter-intuitively, that the overall benefit an increase in raw material use can outweigh the cost saving that would otherwise be achieved. Unexpectedly, the use of a greater amount of material in a folded assembly has been found to be advantageous, and has eliminated the need to have a heat welding station in manufacture. 
     SUMMARY OF THE INVENTION 
     In an aspect of the invention there is a soft-sided insulated container, and a removable liner for placement inside the container. The liner is folded from a monolithic sheet of liner stock to define a chamber, capable of holding liquids. The liner is free of heat welded seams. 
     In another feature of that aspect of the invention the liner is made from a water impermeable plastic sheet. In an additional feature of that aspect of the invention the liner is made from a translucent static cling vinyl sheet. In another additional feature of that aspect of the invention the soft sided insulated container has a base, sides and a top. The liner has a base, sides for placement inside and adjacent to the base and sides of the container. The top of the container is moveable to an open position to permit articles to be placed in the chamber. 
     In still another additional feature of that aspect of the invention the chamber has an opening, the opening having a lip, and the liner is mated to the cooler about the lip. In yet another additional feature of that aspect of the invention the opening has four sides, the lip extends about the four sides opening and the liner is mated to the container on the four sides. In a further additional feature of that aspect of the invention the liner has a rectangular base and four sides extending from the base, each of the sides having an edge adjoining the base and a distal edge distant from the base. The chamber has an opening defined between the distal edges of the sides. 
     In a still further additional feature of that aspect of the invention one of the sides has a lid member extending therefrom, the lid member being moveable to close the opening of the liner. In yet another additional feature of that aspect of the invention the lid member is a flap formed integrally with the liner, the flap having four lid edges, one edge being a folded hinge edge adjoining one of the distal edges of the sides, the remaining three lid edges having a closure for mating with the remaining three distal edges. 
     In another aspect of the invention there is a removable liner for placement inside the container. The liner is formed from a water impermeable plastic sheet. The sheet has a periphery. The liner has a quadrilateral base and four sides extending from the base to define a chamber therebetween capable of holding water. Each of the sides are joined to the base at a base edge. Each of the sides has a pair of lateral edges each meeting the base edge at a corner. Each of the sides has an edge opposed to the base edge and meets each of the lateral edges at a corner. The sheet has corner portions defined between adjacent lateral edges of two of the sides and the periphery and the corner positions are folded to lie against the sides. 
     In a further additional feature of that aspect of the invention the base is a rectangle and two of the sides, joined to the base on opposite sides of the rectangle, are trapezoidal. In a still further additional feature of that aspect of the invention the chamber has the shape of an inverted, truncated rectangular based pyramid. In yet another additional feature of that aspect of the invention the container has an internal face made from a reflective material and the liner is transparent. 
     In another aspect of the invention there is a soft sided insulated container, and a removable liner for placement inside the container. The liner is formed from a water impermeable plastic sheet. The sheet has a periphery. The liner has a rectangular base and four sides extending from the base to form a chamber therebetween, each of the sides being joined to the base at a base edge. The sheet is folded on a first pair of parallel fold lines to define one pair of the base edges. The sheet is folded on a second pair of fold lines to define the remainder of the edges. The sheet has four corner portions each defined between an end portion of one of the first pair of fold lines, an adjacent end portion of one of the second pair of fold lines and the periphery, and the corner portions are folded to lie against the sides. 
     In an additional feature of that aspect of the invention the sides have an inside face and an outside face and the corner portions are folded to lie against the outside faces. In another additional feature of that aspect of the invention each of the corner is folded to form a triangular flap, and each of the flaps is folded to lie against one of the sides. In still another additional feature of that aspect of the invention one of the triangular flaps is folded to lie against each of the sides of the liner. In still yet another additional feature of that aspect of the invention two of the triangular flaps are folded to lie against one side of the liner. In a further additional feature of that aspect of the invention two of the triangular flaps are folded to lie against one side of the liner, and the other two triangular flaps are folded to lie against another side of the liner. 
     In still a further additional feature of that aspect of the invention each of the sides has a distal edge opposed to its respective base edge. The chamber has a lip defined by the distal edges. The corner portions are fastened to the sides adjacent the lip. In still yet a further additional feature of that aspect of the invention one of the sides has a cover flap formed integrally therewith, and joined thereto at a cover fold, the cover flap mating with the distal edges of the remaining sides of the liner. In an additional feature of that aspect of the invention the container has a reflective inner surface and the liner is transparent. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     These aspects and other features of the invention can be understood with the aid of the following illustrations of a number of exemplary, and non-limiting, embodiments of the principles of the invention in which: 
     FIG. 1 is a three quarter view, general arrangement drawing of an insulated container and liner assembly according to the present invention; 
     FIG. 2 is a view of the liner of FIG. 1 taken on an opposite angle; 
     FIG. 3 is a developed view of a liner for use in the assembly of FIG. 1; 
     FIG. 4 is a developed view of an alternative liner for an assembly analogous to the liner of assembly of FIG. 1 in which two sides are tapered; 
     FIG. 5 is a developed view of an alternative liner for an assembly analogous to the liner of assembly of FIG. 1 in which four sides are tapered; 
     FIG. 6 is a developed view of an alternative liner for an assembly analogous to the liner of assembly of FIG. 1 in which the forward side of the assembly is wider than the rearward side; 
     FIG. 7 is a front view of the assembly of FIG. 1 in a collapsed position; 
     FIG. 8 is a rear view of the assembly of FIG. 1 in a collapsed position; 
     FIG. 9 is a side view of the assembly of FIG. 1 in a collapsed position; 
     FIG. 10 is a section showing the wall construction of the assembly of FIG. 1; 
     FIG. 11 a  is a view of an alternative liner for the assembly of FIG. 1; and 
     FIG. 11 b  is a further embodiment of the liner for the assembly of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The description which follows, and the embodiments described therein, are provided by way of illustration of an example of a particular embodiment, or examples of particular embodiments, of the principles of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features of the invention. 
     Referring to the general arrangement illustrations of FIGS. 1 and 2, an example of a preferred embodiment of an insulated container and liner assembly according to the principles of the present invention is indicated generally as  20 . It has two major elements, those being an outer casing in the nature of a soft-sided insulated container  22 , and a removable, impermeable liner  24  for placement inside container  22 . An optional moveable bulkhead, or baffle, in the nature of a partition wall  25  seats within liner  24  for dividing the interior space into two sub-compartments  27  and  29 . 
     Looking at these major elements in detail, it can be seen that container  22  has a bottom  26 , a front panel  28 , a rear panel  30 , and a pair of left and right hand side panels  32  and  34 . In this preferred embodiment the choice of front and rear, left and right, orientations is arbitrary. Each of front panel  28 , rear panel  30 , and left and right hand side panels  32  and  34  is joined at sewn seams to bottom  26  at bottom vertices  36 ,  37 ,  38 , or  39  respectively. Similarly, front panel  28  and side panels  32  and  34  have top edges  40 ,  41  and  42 , distant from their base edges. Rear panel  30  is joined by a folded hinge  44  at its top edge to a top panel in the nature of a lid  46 . Lid  46  has a closure member in the nature of a zipper  48  extending in a U-shape around the three free edge portions of its periphery to mate with the other portions of zipper  48  positioned about the three top edges  40 ,  41  and  42  of panels  28 ,  32  and  34 . Lid  46  is moveable between a closed position, in which zipper  48  may be zipped closed, and an open position in which lid  46  is folded back to permit entry and exit of objects to and from an internal cavity  50  defined between bottom  26  and panels  28 ,  30 ,  32  and  34 . A generally rectangular insulated auxiliary pouch  52  is mounted to the front face of front panel  28 . 
     In the preferred embodiment, lid  46  has an extent substantially equal to that of bottom panel  26 . This need not be the case. Lid  26  could be a small opening set in a larger top panel, or could be an opening of half, or some other portion of the panel. The opening need not extend fully along three sides of lid  26 , but could extend along part of one or two sides as may be found suitable in a particular use. 
     Top edges  40 ,  41 , and  42  form the rim  54  of cavity  50 . On the inside of rim  54  is a liner securing means, or liner attachment mounting, in the nature of a zipper  56 , which, in the embodiment illustrated, includes portions  57 ,  58 , and  59  mounted respectively to panels  28 ,  32 , and  34  near their upper margins, and a hook and eye fabric fastener strip  60  mounted to panel  30 . Although this arrangement is preferred, in an alternative embodiment all of strip portions  57 ,  58 ,  59  and  60  (or some other combination of them) could be hook-and-eye fabric fasteners. Other types of mounting could be used, in addition to zippers, such as interlocking seal strips, snaps, clips, grommets or other means. 
     Container  22 , with liner  24  installed, can be folded to a collapsed position, as shown in FIGS. 7,  8  and  9 . In this collapsed, or storage position, side panels  32  and  34  fold inward, and bottom  26  folds upward. This permits front panel  28  to move toward rear panel  30 . Lid  46  is then drawn forward and downward in front of front panel  28  and auxiliary pouch  52 . Lid  46  has, on its inner face, spaced inwardly from zipper  48 , a retainer in the nature of another hook and eye fastener strip  62  that engages a mating hook and eye fastener strip  64  as best seen in FIG.  1 _located on a lower portion of the front face of auxiliary pouch  52 . In addition, left and right hand side retainers  66  and  68  mounted to the left and right hand edges of auxiliary pouch  52  of front panel  28  are drawn around to fasten to fastening strips  70  and  72  located on the outer, rearward face of rear panel  30 . (When container  22  is in its open position, side retainers  66  and  68  engage storage strips  74  and  76  located on side panels  32  and  34  respectively). 
     Other features of container  22  are visible in FIGS. 1 and 2. Front and rear carrying handles  78  and  80  with reinforced bails are attached to both front panel  28  and rear panel  30  to permit two people to carry assembly  20  between them. In the preferred embodiment assembly  20  has a maximum capacity of  24  quarts. Smaller embodiments, include a twelve quart container. A single shoulder strap  79  is attached to side panels  32  and  34 . An elasticized retaining matrix  82  permits other materials, such as cups, plates, serving utensils or other objects to be carried on top of assembly  20 . Above strip  64 , auxiliary pouch  52  has a see-through mesh pocket  84 , such as may be convenient for carrying knives, forks, spoons or other objects. 
     FIG. 10 shows a cross section of front panel  28  with liner  24  in place. A scab section of panel  34  is also shown to reveal its layers of construction. With the exception of auxiliary pouch  52 , this section is typical not only of front panel  28  but also, generally, of rear panel  30 , side panels  32  and  34 , bottom  26  and lid  46 . The outer facing layer of front panel  28  is a canvas covering layer  88  for resisting abrasion. It overlays a closed cell foam insulation layer  90 . The inner face of insulation layer  90  is covered by flexible plasticised metallic foil sheeting  92  that is shiny and reflective. The material is sold under the name Therma-Flect (T.M.). Liner  24  lies inside sheeting  92 , and is pressed against it by the objects it contains. The inside of pouch  52  is lined with white vinyl sheeting,  93  on its forward and bottom sides. 
     Liner  24  is shown in FIGS. 1,  2  and  3 . It is made from a membrane, or web, in the nature of a sheet  100  of flexible, transparent plastic stock, in particular, static cling vinyl. The shiny, reflective surface of sheeting  92  is visible through liner  24  in use. Liner  24  has a base  102  and four sides, front, rear, left hand and right hand respectively,  104 ,  106 ,  108 , and  110  extending upwardly from base  102 . Each of sides  104 ,  106 ,  108  and  110  is joined to base  102  at a base edge,  112 ,  114 ,  116  or  118 , as indicated, and each has an opposite, distal edge  120 ,  122 ,  124  or  126  distant from its respective base edge. The sides meet at respective upstanding corners  128 ,  130 ,  132  and  134 . A chamber  136  is defined between base  102  and sides  104 ,  106 ,  108  and  110 . Chamber  136  has an opening  138  defined by the peripheral lip  140  formed collectively by the distal edges  120 ,  122 ,  124  and  126  of sides  104 ,  106 ,  108  and  110 . Immediately below lip  140  liner support fasteners, in the nature of hook and eye strips, are mounted to sheet  100 . This mounting may be by heat welding or by use of a bonding agent or adhesive. In the preferred embodiment lip  140  is folded over to form a hem, and fasteners  141 ,  144 ,  143  are of the nature of a continuous zipper around three sides of lip  140 , and a fastener  142  in the nature of a fabric hook-and-eye strip are sewn in place with stitching  145  that is at a height relative to base  102  that is expected to be well above the liquid level in liner  24 . 
     In an alternate embodiment, fasteners  141 ,  142 , and  143  are all fabric hook and eye fasteners each mounted on one side of lip  140 , and which mate with corresponding hook-and-eye fastener strips mounted to container  22 . These fastener strips are commonly sold under the name Velcro (T.M.). Optional partition  25  is variably positionable. About the upper portion of its periphery it has a strip engaging material  146  that catches on mating strips  147  and  148  located on the inner face of liner  24 . These strips can be hook and eye fastener strips. The range of the strips permits the division of sub compartments  27  and  29  of chamber  136  into equal, half-and half portions, or into some other portions, such as ¼ to ¾, ⅔ to ⅔, ⅖ to ⅗ and so forth as may be found desirable given the objects to be contained in chamber  136 . 
     In FIG. 3 sheet  100  is shown in developed view, as it would be before being folded to form liner  24 . A first pair of parallel fold lines  150  and  152  extend across sheet  100 , and a second pair of parallel fold lines  154  and  156 , perpendicular to lines  150  and  152  extend along sheet  100 , thus dividing it into nine portions within the rectangular periphery,  158 , of sheet  100 . It will also be noted that each of lines  150 ,  152 ,  154  and  156  has two intersections, and is thus divided into a central sector between the parallel lines it intersects, and a pair of end sectors between each of the parallel lines it intersects and the line&#39;s termination at periphery  158 . 
     The central portion of sheet  100 , bounded by the central sector of each of lines  150 ,  152 ,  154  and  156 , defines base  102 , each of those sectors defining one of base edges  112 ,  114 ,  116  and  118 . Front side  104  is defined between the central sector  160  of line  150 , two parallel forward end sectors  162  and  164  of lines  154  and  156 , and a mid-edge sector  166  of periphery  158 . Rear side  106  is defined by the central sector  168  of line  152 , two parallel rearward end sectors  170  and  172  of lines  154  and  156 , and a mid edge sector  174  of periphery  158 . Left hand side  108  is defined by central sector  176  of line  154 , two left end sectors  178  and  180  of lines  150  and  152 , and a mid-edge sector  182  of periphery  158 . Right hand side  110  is defined by central sector  184  of line  156 , two right end sectors  186  and  188  of lines  150  and  152 , and a mid-edge sector  190  of periphery  158 . 
     The remaining four portions of sheet  100  are corner portions  192 ,  194 ,  196  and  198  defined by a pair of adjacent end sectors of a pair of perpendicular lines, and a corner sector of periphery  158 , indicated respectively as  202 ,  204 ,  206  and  208 . Corner portions  192 ,  194 ,  196  and  198  are bisected by diagonal bisectors  212 ,  214 ,  216  and  218  which extend from the intersection of the respective perpendicular lines to periphery  158 . 
     Having thus defined the geometry of sheet  100 , liner  24  is formed by folding sides  104 ,  106 ,  108  and  110  upwardly such that sectors  162  and  178 ,  164  and  188 ,  170  and  180 , and  172  and  186  lie adjacent to each other to form corner  128 ,  130 ,  132  and  134  respectively. This folding necessitates folding of corner portions  192 ,  194 ,  196  and  198 , and this is done along their respective diagonal bisectors. 
     When folded along bisectors  212 ,  214 ,  216  and  218  corner portions  192 ,  194 ,  196  and  198  form triangular flaps  220 ,  222 ,  224  and  226  as best seen in FIGS. 1 and 2. In the preferred embodiment flaps  220  and  222  are folded to lie against the outside face of front side  104 , the corner of flap  220  lying most distant from corner  128  overlapping the corner of flap  222  lying most distant from corner  130 . Similarly flaps  224  and  226  are folded to lie against the outside face of rear side  106  the most distant corner of flap  224  overlapping the most distant corner of flap  226 . One edge of each flap lies roughly flush with lip  140 , which is folded over and the entire periphery of opening  138  of chamber  136  sewn as a hem  228  having a double row of stitches. In this way liner  24  is formed from sheet  100  such that it is not only free of welded seams, but free of any seams below hem  228  of lip  140 . 
     In the preferred embodiment the folding process is purely mechanical, and can be performed relatively quickly, in contradistinction to heat welding or adhesive bonding processes which requires a time interval for heating and cooling or for adhesive curing. In as much as the preferred embodiment uses a relatively thick static cling vinyl, sheet  100  can be folded over a cube form of the desired dimensions, and held in place by its own clinging properties in preparation for the sewing of hem  228 . The overlap of the tips of flaps  222  and  224 , and flaps  226  and  228 , and subsequent sewing makes it doubly improbable that liner  24  will unfold. 
     Liner  24  is formed from a single integral sheet, and, absent punctures of that sheet is not intended to leak below the level of the sewn seam at lip  140 . The body of base  102  and sides  104 ,  106 ,  108  and  110  is seamless, being free of heat welds or other joints. In general use the liquid level in chamber  136  is not expected to be greater than one half of the height of the sides, and still less commonly to be more than three quarters of the height. There are no seams below either of these levels, heat welded or otherwise. 
     Liner  24  is also thin enough that it can be folded inside container  22  when container  22  is compressed to its collapsed position as illustrated in FIGS. 7,  8 , and  9 . Liner  24  need not be transparent, but could be translucent or opaque. A transparent liner is preferred since it permits the reflection of sheeting  92  to be seen. 
     In an optional embodiment, a liner  224  can have its own closure, or lid,  230 , to provide a double closure with lid  46  of container  22  in FIG. 11 a . As shown in FIG. 11 a , optional lid  230  extends on a folding plastic hinge  232  that is an integral part of sheet  234  from rear side  236  of sheet  234 , and mates at front, left hand and right hand side edges  238 ,  240  and  242  along a U-shaped closure interface such as may be held closed by a closure member in the nature of a seal, a zipper, a hook and eye fabric fastener, or a similar device. It is not necessary that the opening of the container, or the liner, form a parallel plane to the respective base or bottom sides. The opening could be in a skewed plane, or could be something other than a plane. 
     In alternative embodiments, one of each of corner flaps  220 ,  222 ,  224  and  226  can be folded against each of sides  104 ,  106 ,  108  and  110  as shown in FIG. 11 b , or a pair ( 220 ,  224 ) can be folded against left hand side  108  and another pair ( 222 ,  226 ) against right hand side  110 , rather than against front and rear sides  104  and  106  as illustrated in FIG. 11 a . It is not necessary that the corner portions have one edge lying flush with lip  146 . However, if the corner portions are cut down, the height at which a liquid tight barrier is provided may not necessarily be as high as shown in the preferred embodiment of FIG.  1 . It is also not necessary that corner portions  192 ,  194 ,  196 , and  198  be folded against the outside faces of the sides, but could be folded to lie along the inside faces. It would also be possible to fold each flap to lie partially against one side and partially against another side by using more than one fold line and by cutting the periphery of the corner portions differently. There is simplicity in using a single fold and to fold the flaps against the outside of one side of the liner, as shown in the preferred embodiment of FIG.  1 . 
     As shown in the developed views of the alternate embodiments of FIGS. 4,  5 , and  6 , the liner need not be a cube or cuboid, but could be a tapered, trapezoidal, or truncated pyramidal shape. In the embodiment of FIG. 4 a developed sheet  300  has fold lines for forming a liner having a pair of opposed trapezoidal sides  304  and  306  which rise at right angles from a base  308 , and a pair of opposed rectangular sides that are folded upward at an angle corresponding to the rake angle a of trapezoidal sides  304  and  306 . It can be seen that there is one pair of parallel fold lines  310  and  312 , each line having a central sector  314 ,  316  and a pair of left and right end sectors  318 ,  320  or  322 ,  324 . There is also a pair of fold line sectors  326  and  328  which define the remaining two sides of base  308  (perpendicular to sectors  314  and  316 ). The intersections of sectors  326 ,  314 ,  328 , and  316  define the corner of base  308 . Extending away from those corner to periphery  330  are left and right hand canted trapezoidal side sectors  332 ,  334 ,  336 , and  338  to define the remaining vertices of trapezoidal sides  304  and  306 . At the angular bisector of the included angle between adjacent pairs of rectangular side lateral sectors and trapezoidal side sectors, as, for example between sectors  318  and  332 , are corner portion fold lines  340 ,  342 ,  344 , and  346 . Corner portions  348 ,  350 ,  352  and  354 , each defined between one trapezoidal side end sector, one rectangular side end sector and periphery  330 , have been trimmed along periphery  330  to lie flush with the resulting lip. When sheet  300  is folded in a manner analogous to the folding of sheet  100 , a cradle shaped liner will result, for mating use with a similarly cradle shaped container analogous to container  22 . 
     In the embodiment of FIG. 5 a developed sheet  400  has fold lines for forming a liner  402  having a first pair of opposed trapezoidal sides  404  and  406  which rise at a non-perpendicular angle φ from a base  408 , and a second pair of opposed trapezoidal sides  410 ,  412  that are folded upward at an angle corresponding to the vertical projection of the rake angle β of the first pair of trapezoidal sides  404  and  406 . It can be seen that there is one pair of fold line sectors  414 ,  416  and a perpendicular pair of fold line sectors  426  and  428  which define the remaining two sides of base  408 . The intersections of sectors  426 ,  414 ,  428 , and  416  define the corner of base  408 . Extending away from those corner to periphery  430  are left and right hand trapezoidal side lateral sectors  418 ,  420 ,  422  and  424 . Similarly, left and right hand canted trapezoidal side sectors  432 ,  434 ,  436 , and  438  extend from those intersections toward periphery  430  to define the remaining vertices of the trapezoidal sides. At the angular bisector of the included angle between adjacent pairs of rectangular side lateral sectors and trapezoidal side sectors, as, for example between sectors  418  and  432 , are corner portion fold lines  440 ,  442 ,  444 , and  446  of corner portions  448 ,  450 ,  452  and  454 . 
     Sectors  418 ,  420 ,  422 ,  424 ,  432 ,  434 ,  436  and  438  all have the same true length, indicated as I. The distance that sectors  418 ,  420 ,  422  and  424  are splayed outward from square is indicated as ε. Similarly, the distance that sections  432 ,  434 ,  436  and  438  are splayed outward from square is indicated as δ. Angle (φ satisfies the condition that Sin φ=(ε/(l 2 −δ 2 ))½. Similarly Angle β satisfies the condition that Sin β=(δ(I 2 −δ 2 ))½. 
     When folded in a manner analogous to the folding of sheet  100 , sheet  400  will form a truncated, inverted rectangular shaped pyramid. It should be noted that the pairs of opposed slanted pyramid sides need not rise at the same angle, but could be at different angles. In the most general case, each side could rise at a different angle, and to a different height. The upper edges of the sides need not be level, but could have a slant, or, alternatively, need not be linear but could be curved as may suit the desired geometry. However, it is expected that the sides will, most often, have straight and level edges. 
     In the embodiment of FIG. 6, a developed sheet  500  has fold lines for forming a liner  502  having a trapezoidal base  504  such as might be desired in a knapsack having a large rearward face for placement against a person&#39;s back, and a narrower outer or forward face. A pair of parallel lines of unequal length, being a short front fold line  506  and a longer rear fold line  508 , define the parallel sides of the trapezoidal base  504 . A pair of left and right hand side fold lines  510  and  512  extend between lines  506  and  508  at angles to define the splayed sides of trapezoidal base  504 . Front side  514 , rear side  516 , left side  518  and right side  520  are all hinged along respective fold lines  506 ,  508 ,  510  and  512  to base  504 . Corner portions  522 ,  524 ,  526  and  528  are defined between the periphery  530  and respective pairs of side sectors  532  and  534 ,  536  and  538 ,  540  and  542 , and  544  and  546 . Each of portions  522 ,  524 ,  526  and  528  has a fold line  548 ,  550 ,  552  or  554  on which the respective corner portion is folded, those portions being trimmed along their peripheral edges to lie flush with the peripheral edges of the respective sides against which they are folded, similar to the manner described above in connection with the preferred embodiment. 
     A preferred embodiment has been described in detail and a number of alternatives have been considered. As changes in or additions to the above described embodiments may be made without departing from the nature, spirit or scope of the invention, the invention is not to be limited by or to those details, but only by the appended claims.