Patent Publication Number: US-6342693-B1

Title: Resizable microwave oven liner apparatus and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/374,358, filed Aug. 13, 1999, Pat. No. 6,137,097. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the fields of protective coverings, and specifically, to protecting a microwave oven from food spills and spatter. 
     BACKGROUND OF THE INVENTION 
     Microwave ovens are widely used all over the world to heat and cook food items much more rapidly than conventional heating ovens. But the nature of microwave technology is such that in the process of heating food items, the microwaves will often cause the food items to overflow, or to “pop,” which of course, produces a mess along the sides, back and front (interior surface) of the microwave oven that needs to be cleaned with a sponge or similar cleaning apparatus. This entails reaching into the oven and applying “elbow grease” at various awkward angles, and as anyone who uses and has ever had to clean a microwave oven is aware, is tiresome and difficult. 
     The U.S. Patent literature does disclose some efforts to solve this problem. U.S. Pat. Nos. 4,721,140; 4,785,160; 4,797,523; 4,801,773; and 4,950,859, for example, all disclose various containers, covers, shields, etc., that are placed over or around a particular food item being cooked, in order to block and prevent spills and spatters from that food item from reaching the inner surface of the microwave oven. But these are associated in their use with each individual food item being cooked, rather than with the microwave oven itself. As such, these devices are removed along with the associated food item each time a food item is heated or cooked, and reintroduced into the microwave oven each time a new food is to be cooked. 
     U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 improve this situation, since these protective devices are each used in connection with the microwave oven itself, and remain in place to guard against spills and spatter from the cooking of one food item to the cooking of subsequent foods items. After a time, once the protective device has become soiled beyond a certain point, the device is removed and disposed of, and is replaced with a new, similar device. 
     But microwave ovens are manufactured and sold in many varied sizes, and all of U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 suffer the common deficiency that they cannot easily be used in connection with varying sizes of microwave oven. Indeed, a survey taken by applicants of over  100  microwave oven models reveals that microwave ovens typically vary in volume from about 0.5 to 1.8 cubic feet, and in linear dimension from a minimum height of about 6 inches to a maximum height of about 15 inches, from a minimum width of about 11 inches to a maximum width of about 21 inches, and from a minimum depth of about 10 inches to a maximum depth of about 18 inches. This survey also reveals that these linear dimensions typically vary by ¼ inch, ⅛ inch, ⅙ inch, or {fraction (1/16)} inch increments. Given this wide size variability from one microwave oven to the next, it would be difficult or impossible to use the protective devices of U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 for more than a single size of microwave oven, give or take perhaps a fraction of an inch along any one linear dimension. As such, if these protective devices were to be used for all commonly-manufactured oven sizes, it would be necessary to manufacture dozens of different sizes of these protective devices. 
     In addition, all of these liners are difficult to set up and attach for use inside the microwave oven, and (e.g., U.S. Pat. Nos. 4,778,968, column 2, lines 58-61) even need an independent support structure. 
     These liners also do not appear to provide suitable protection for the front door of a microwave oven. 
     Additionally, the choice of materials used to construct a microwave oven liner is very important. Saran-type polymeric materials do not hold up well over time and are meant for one use and then disposed of. They do not have a heat history at all, melting in the presence of steam resulting from cooking food. Cardboard-type material and papers commonly used in paper bag construction are not appropriate either. These materials absorb moisture and spilled foods. This causes them to stick to the microwave interior, defeating their purpose and usefulness. 
     OBJECTS OF THE INVENTION 
     It would be desirable therefor, to provide a microwave oven liner which can be configured (resized or scaled) to protect a wide range of microwave oven sizes, encompassing at least the size ranges noted in the background of the invention. 
     It would further be desirable if this resizing could be achieved at various small increments, permitting the microwave oven liner to be resized to any height from about 6 inches to 15 inches, and to any width from about 11 inches to about 21 inches, and to any depth from about 10 inches to about 18 inches by, for example, not limitation, ⅛ inch increments. 
     It would further be desirable to provide a simple means to attach the microwave oven liner to the microwave oven, once it has been resized to the dimensions appropriate to the given microwave oven for which it is to be used. 
     It would further be desirable to provide a means for protecting the front door of a microwave oven, in addition to protecting the sides, top, bottom, and back of the microwave oven. 
     It would further be desirable to provide a microwave oven liner which is fabricated from a material which has structural integrity and is able to free-stand in the microwave device on its own, requiring minimal or no supports, and without imposing undue setup requirements upon the liner user. 
     It would further be desirable for the liner to be durable under repeated microwave bombardment and heating, so that the liner remains free-standing after many microwave uses, and needs to be disposed of because of the spilled food that it has prevented from being caked on the microwave surface—not due to the liner becoming deformed from heat. 
     It would further be desirable for the microwave oven liner not to allow food to be absorbed or soaked into its surface, as this would cause the liner to stick to the microwave surface, defeating its purpose. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the invention disclosed herein is a pleated microwave oven liner comprising a plurality of semi-rigid liner pleats that enable the microwave oven liner to be expanded from initial dimensions of approximately 6 inches in height by 11 inches in width, to final dimensions as large as approximately 15 inches in height by 21 inches in width, for example, not limitation, by ⅛ inch increments. As such, a single microwave oven liner can be produced which is suitable for use in microwave ovens over a wide range of varying sizes. The depth is varied from approximately 10 inches to 18 inches either by folding over the front of the liner on itself, or by removing part of the front of the liner, e.g. by cutting the liner, or by tearing the liner along perforated tear lines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The features of the invention believed to be novel are set forth in the appended claims. The invention, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawing(s) in which: 
     FIG. 1 is a top-rear-right side perspective view illustrating a resizable microwave oven liner in a preferred embodiment of the invention, in a fully collapsed state with all of its pleats closed. 
     FIG. 2 is a top-rear-right side perspective view illustrating the resizable microwave oven liner of FIG. 1, in a fully expanded state with all of its pleats opened. 
     FIG. 3 is a top-front-right side perspective view illustrating the resizable microwave oven liner of FIG. 1, in a partially expanded state with its pleats partially opened, and illustrating in detail, the pleating apparatus and method according to said preferred embodiment of the invention. 
     FIG. 4 is an exploded plan view illustrating single, partially opened pleats from FIG.  3 . 
     FIG. 5 is a perspective view illustrating the placement of the microwave oven liner of FIG. 1 into a microwave oven, as well as a separate microwave door liner used to protect the inside of the front microwave oven door. 
     FIG. 6 is an upper-front-left perspective view of an alternative preferred embodiment of the invention wherein the microwave oven liner comprises four or five distinct sections without any pleating structure. 
     FIG. 7 is an upper-front-left perspective view of an alternative preferred embodiment of the invention wherein the microwave oven liner comprises two distinct section with a single pleat for vertical expansion, in its fully collapsed state. 
     FIG. 8 is an upper-front-left perspective view of the embodiment of FIG. 7, in its fully expanded state. 
     FIG. 9 is an upper-front-left perspective view of a third preferred embodiment which schematically illustrates the microwave oven liner comprising a unitary structure with a single pleat for vertical expansion, and a single pleat for horizontal expansion, in its fully collapsed state 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a top-rear-right side perspective view microwave oven liner  1  in a fully collapsed (unexpanded) state according to a preferred embodiment of the invention. In this fully collapsed state, microwave oven liner  1  has a height  11  of approximately 6 inches, a width  12  of approximately 11 inches, and a depth  13  of approximately 18 inches. The height and width are chosen to correspond with the smallest sizes of commonly-available microwaves as outlined above; the depth corresponds with the largest of such sizes. Toward its rear region (shown toward the right side of FIG.  1 ), microwave oven liner  1  comprises a rear surface comprising a “pyramid” surface with a linear dimension of approximately 7.5 inches along height expansion region  14  (a similar region, not marked with a reference numeral, exists on the opposite, lower face of the pyramid), and a linear dimension of approximately 10.5 inches along width expansion region  15  (as similar region, also not marked, exists on the opposite face of the pyramid). 
     Microwave oven liner  1  comprises a plurality of pleats  102  running horizontally along its top surface  16 , its bottom surface  17 , its left surface  18 , and its right surface  19 , substantially in the direction illustrated, as well as a front opening  108  which is fully open. Each pleat continues on through the pyramid surface to a pleat gathering point  104  comprising the tip (apex) of the aforementioned pyramid (at the rear of microwave oven liner  1 , which again, is shown toward the right side of FIG.  1 ). 
     Microwave oven liner  1  also comprises a plurality of optional depth adjustment lines  106 , such as but not limited to pre-cut perforations, which are used to adjust depth  13  of microwave oven liner  1 . As illustrated, depth adjustment lines  106  run from left sides of top  16  and bottom  17  surfaces to right sides of top  16  and bottom  17  surfaces, and from tops of left  18  and right  19  side surfaces to bottoms of left  18  and right  19  side surfaces. The function of depth adjustment lines  106  will be further described in detail below, but it is to be observed at this point, if microwave oven liner  1  were to be cut along the rightmost depth adjustment line  106 , that its depth would be reduced from approximately 18 inches to approximately 10 inches, which is the smallest depth of commonly-available microwaves. 
     Finally, microwave oven liner  1  comprises unpleated regions  110  along a central region of top surface  16  and a central region of bottom surface  17 . It is to be noted that the lines  102  as illustrated in FIG. 1 representing the pleats do not illustrate the actual pleats themselves (which will be illustrated and discussed in further detail in connection with FIG.  3 ), but rather, the regions of microwave oven liner  1  which comprise the pleats, as well as the direction along which the pleats run along microwave oven liner  1 . 
     FIG. 2 illustrates the resizable microwave oven liner of FIG. 1, in a fully expanded state with all of its pleats opened. In its fully expanded state, microwave oven liner  1  now has a height  11  of approximately 15 inches (as opposed to approximately 6 inches in its fully collapsed state), and a width  12  of approximately 21 inches (as opposed to approximately 11 inches in its fully collapsed state). The depth  13  remains at 18 inches, but again, this depth is reduced by cutting or tearing microwave oven liner  1  (or folding it over on itself) along one of the depth adjustment lines  106 . Again, by using the rightmost depth adjustment line  106 , this depth is reduced to the 10 inch depth of the smallest-depth microwaves commonly available. 
     In this fully expanded state, the pyramid surface of FIG. 1 has become substantially flattened, because the “excess” liner material along height expansion region  14  and width expansion region  15  has been used to expand the rear of microwave oven liner  1  over the 9 inch expansion in height from 6 to 15 inches, and the 10 inch expansion in width from 11 to 21 inches. It can now be understood why height expansion regions  14  are chosen to be 7.5 inches, as this provides the necessary rear expansion liner material to allow the liner height to be expanded to 15=2 ×7.5 inches. It is similarly understood why width expansion regions  15  were chosen to be 10.5 inches, since this provides the necessary rear expansion liner material to allow the liner width to be expanded to 21=2×10.5 inches. In short, the two height expansion regions  14  are chosen such that their total length is approximately equal to the height of microwave oven liner  1  in its fully-expanded state, and the two width expansion regions  15  are chosen such that their total length is approximately equal to the width of microwave oven liner  1  in it fully-expanded state. As FIGS. 1 and 2 are drawn roughly to scale with one another, it is to be observed that the distances between pleat  102  lines is larger in FIG. 2 than in FIG. 1, which serves to represent the expansion that has taken place of the pleated sections. Again, these lines do not yet show the pleats themselves. 
     FIG. 3 shows microwave oven liner  1  from a top-front-right perspective view. In this view, microwave oven liner  1  is partially expanded, and pleats  102 , shown in detail here, are partially expanded. FIG. 4 illustrates single pleats  102  in more detail, in their partially-expanded states of FIG.  3 . Toward the left of FIG. 4, is a single horizontal pleat, which is representative of a pleat along either the top surface  16  or bottom surface  17  of microwave oven liner  1 . Toward the right of FIG. 4, is a single vertical pleat, which is representative of a pleat along either the left surface  18  or right surface  19  of microwave oven liner  1 . The reasons for the difference between vertical and horizontal pleats will become apparent below; but it is worth noting for now that in the preferred embodiment, liner width  12  needs to be expandable from approximately 11 to 21 inches, which is less than a doubling of the width. In contrast, the height  11  needs to be expandable from approximately 6 to 15 inches, which is more than a doubling of the height, and in fact, is a 2.5-fold increase in height. In the partially-expanded state of FIG. 3, the pyramid near the rear of microwave oven liner  1 , which cannot be seen from this view, is somewhat less-pronounced than it is in FIG. 1, but is not yet fully flattened as in FIG.  3 . 
     Referring to FIG. 4, outer pleat surface  41  for a horizontal pleat  102 , in the preferred embodiment, is chosen to be approximately ¼ inch in length, and pleat expansion surfaces  42  are chosen to be approximately ⅛ inch in length. Thus, as a single pleat  102  is unfolded from its fully collapsed state to its fully expanded state, this unfolding will add an extra ¼ inch =2×⅛ inch to the overall width of microwave oven liner  1 , and the individual pleat  102  will itself unfold from ¼ inch to ½ inch, i.e., it will double in size. As it is desired in the embodiment of FIGS. 1 through 3 to expand the width to be anywhere from 11 inches to 21 inches, i.e., a total up to 10 inches, a total of 40=10/(2×⅛) pleats  102  are necessary along liner width  12 . These 40 pleats, when fully collapsed, are ¼ inch each, and will thus yield a total of 10=40×¼ inches in liner width  12 . The extra 1 inch, is provided by unpleated regions  110 , bringing the unexpanded width to 11=10+1 inches. When these 40 pleats are fully expanded, they will double in size to ¼ inch each, and will thus yield a total of 20=40×¼ inches in liner width, with the extra 1 inch from unpleated regions  110  bringing the fully-expanded width of 21=20+1 inches. It is assumed here, and throughout, that each pleat  102  is adjacent to the next pleat  102  as closely as possible, but without overlap. Of course, the above described configuration is illustrative only, and can obviously be varied by someone ordinary skill in the art, within the scope of this disclosure and its associated claims. 
     In contrast, pleats  102  along height  11  of microwave oven liner  1  take the form of the pleat shown toward the right of FIG. 4, and include, for example, a pleat extender section  43  comprising additional material that enables each pleat to expand by a factor of greater than 2 to 1. This is because the height  11  of microwave oven liner  1 , in order to accommodate all conventional microwave sizes, must increase from 6 to 15 inches. It is apparent on close inspection, that the pleats shown toward the left of FIG. 4 can gain at most a 2 to 1 expansion, and that simple adding more pleats will not resolve this, but will merely increase the unexpanded height  11  of microwave oven liner  1  beyond the desired 5 inches. 
     Thus, the vertical pleats  102  are similar to the earlier-described horizontal pleats  102 , but comprise added pleat extender sections  43  comprising two halves of approximately {fraction (1/16)} inch in length apiece. When these pleats—which start off in their contracted state at ¼ inch apiece—are fully expanded, they gain ¼ inch=2×⅛ inch from each of the two pleat expansion surfaces  42 , as well as an additional ⅛ inch=2×{fraction (1/16)} inch from each of the pleat extender sections  43 . Thus, the overall gain per pleat is ⅜ inch=¼ inch (from  42 )+⅛ inch (from  43 ), and each pleat thus expands from ¼ inch to ⅝ inch=¼ inch+⅜ inch. This is a gain of 2.5 to 1 (i.e., ⅝ to ¼) per pleat, which mirrors the overall gain need to go from 6 inches to 15 inches in height  11 . Thus, with a total of 24 such pleats  102 , one can expand from 6 inches=24 pleats×¼ inch per pleat, to 15 inches=24 pleats×⅝ inch per pleat. Here, no unpleated region such as  110  is needed. 
     It is to be noted that FIG. 3 actually shows approximately 20 pleats along width  12 , and approximately 18 pleats along height  11 . This is done simply to avoid overcrowding the drawing; thus if all of the aforementioned dimensions for the preferred embodiment of FIGS. 1 through 3 are to be employed in a particular reduction to practice, FIG. 3 actually illustrates approximately one pleat horizontal pleat to represent approximately every two horizontal pleats that are needed for the reduction to practice, and approximately 3 vertical pleats for every 4 that are needed for reduction to practice. Alternatively, for example, if outer pleat surface  41  were chosen to be ¼ inch, pleat expansion surfaces  42  were chosen to be ¼ inch, and the two halves of pleat extender sections  43  were chosen to be approximately ⅛ inch in length apiece, then FIG. 3 would illustrate substantially a one-to-one correspondence between the number of pleats required, and the number represented in FIG.  3 . 
     The ⅛ inch pleat expansion surfaces  42  and {fraction (1/16)} inch pleat extender sections  43  are chosen for the preferred embodiment, since they provide expansion in ⅛ inch increments if half of a single pleat  102  is unfolded, in ¼ inch increments if an entire pleat  102  is unfolded and in ⅜ inch increments if a pleat extender sections  43  is also unfolded. This is desirable since the dimensions of commonly-available microwaves typically vary in ⅛ or ¼ inch increments, and this provides greater incremental expansion capability. 
     It will be obvious to someone of ordinary skill how to vary and generalize all of the aforementioned choices of pleat dimension as well as the number of pleats, at will, to provide any desired overall expansion of height  11  and width  12  for microwave oven liner  1 . Any such variation or generalization is considered to be within the scope of this disclosure and its associated claims. In particular, the choice of having height  11  vary from 6 inches to 15 inches, width  12  vary from 11 inches to 21 inches, and depth  13  vary from 10 inches to 18 inches, is not made in the abstract; but is made to accommodate the sizes of microwaves as they are customarily manufactured. If microwaves were to be manufactured which exceed one or more of the maximum dimensions noted above, or are smaller along one or more of the minimum dimensions noted above, then the specifications for microwave oven liner  1  can easily and obviously be varied to accommodate this. Similarly, once the suitable maximum and minimum dimensions have been specified for microwave oven liner  1 , one can vary the individual pleat  102  specifications as desired, recognizing the simple and obvious generalizations of the relationships among individual pleat characteristics, number of pleats, and desired size ranges, as outlined above for the preferred embodiment outlined above and chosen by way of example only, not limitation. 
     Similarly, depth adjustment lines  106  are for illustration only, and may be incorporated into microwave oven liner  1  as desired. For example, not limitation, these can be separated by ¼ or ⅛ inch from one another to accommodate the ¼ or ⅛ inch depth increments that are typical in commonly-available microwave ovens. And the range of depth from 10 inches to 18 inches that is achieved by these depth adjustment lines  106  is again based on the depth of commonly-available microwave ovens. If ovens with larger depths than 18 inches, or smaller depths than 10 inches, were to become available, it would be obvious how to modify the specifications for microwave oven liner  1  in order to accommodate this. 
     FIG. 3 also illustrates a turntable aperture  31  along unpleated region  110  of bottom surface  17  through which the spindle of a microwave turntable can pass when microwave oven liner  1  is placed into a microwave oven  5  (see FIG.  5 ). Also illustrated is a pleat gathering means  32  proximate a pleat gathering point  104 , which may comprise, for example, not limitation, a microwave-safe (e.g. plastic, ceramic) staple or constricting ring designed to hold together the pleats  102  near the pyramid apex so that they do not fall apart toward the rear of the liner as microwave oven liner  1  is being expanded. It is to be observed that the pleats  102  along the pyramid surface of microwave oven liner  1  are simply extensions of the pleats  102  along the top  16 , bottom  17 , and sides  18  and  19  of microwave oven liner  1 , gathered together to all join up and be gathered together at pleat gathering point  104 . 
     FIG. 5 illustrates the placement of microwave oven liner  1  into a microwave oven  5 . Prior to placing microwave oven liner  1  into microwave oven  5 , pleats  102  are unfolded until microwave oven liner  1  is enlarged to accommodate the height and width of the particular microwave oven  5  with which the liner is to be used. FIGS. 1 through 3 of course, illustrate microwave oven liner  1  at various stages of expansion, from fully-contracted (FIG. 1) through partially-expanded (FIG.  3 ), through fully-expanded (FIG.  2 ). If microwave oven liner  1  includes optional depth adjustment lines  106 , then microwave oven liner  1  is also torn, cut or folded over itself along a chosen depth adjustment line  106  to size microwave oven liner  1  to the depth necessary to accommodate the microwave oven  5  for which it is being used. If optional depth adjustment lines  106  are not included, then microwave oven liner  1  is still folded in on itself to the necessary depth, or, alternatively, is cut to the proper depth using commonly-available cutting means such as, but not limited to, scissors. The term “depth reduction means” as used herein, refers to any suitable means used to reduce the depth of microwave oven liner  1 , including, but not limited to, depth adjustment lines  106  earlier discussed, cutting by any suitable cutting means even in the absence of depth adjustment lines  106 , folding the liner over on itself even in the absence of depth adjustment lines  106 , etc. 
     Once the height  11 , width  12  and depth  13  of microwave oven liner  1  are adjusted to fit microwave oven  5 , microwave oven liner  1  is then inserted into microwave oven  5  as shown. Liner-to-oven securing means  51  are placed upon and attached to microwave oven liner  1  at one or more suitable securing locations, and then, as microwave oven liner  1  is inserted into microwave oven  5 , are pressed against and attached to the inside surface of microwave oven  5  on the top, bottom, side and/or rear interior walls of microwave oven  5 . Liner-to-oven securing means  51  may be, for example, not limitation, double sided tape separate from microwave oven liner  1 , or tape already pre-attached to microwave oven liner  1  at one or more suitable securing locations. During this insertion process, if microwave oven  5  has a turntable, the turntable is removed, turntable spindle aperture  31  is placed over the turntable spindle  52  upon which the turntable rests, and the turntable is then placed back upon the spindle. The rear, pyramid surface of oven liner  1  is “scrunched” as necessary against the rear of the microwave oven so that it is substantially flush against the rear of the microwave oven, irrespective of how large or small the pyramid might be. 
     At this point, the top, bottom, rear, and both side interior walls of microwave oven  5  are protected from spatter by microwave oven liner  1 . But it is also desirable to protect microwave oven front door  53 . An optional front door liner sheet  54 , separate from oven liner  1 , is used for this purpose. Front door liner  54  is simply attached to microwave front door  53  as shown, also using liner-to-oven securing means  51 . Because most microwave oven front doors  53  have a window through which the inside of microwave oven  5  can be viewed from outside while front door  53  is closed, in the preferred embodiment, front door liner  54  is transparent so as to not obstruct this view. 
     Many microwave ovens  5  also contain a platform (not shown) attachable to platform support brackets (not shown) on the rear and sides of microwave oven  5 . Such a platform is used to support a food item being heated substantially near the center of the oven. If microwave oven  5  contains such a platform and platform supports, microwave oven liner  1  is also pressed firmly over these supports and deformed or torn at the support region such that the supports, or the shape of the supports, will protrude through microwave oven liner  1  in order to support the platform. The platform is then placed over the supports, or over the sections of microwave oven liner  1  that envelop these supports. 
     It is also understood, while microwave oven liner  1  shows all of a pleated top surface  16 , bottom surface  17 , left surface  18 , right surface  19 , and rear surface comprising the pyramid surface earlier shown and described, that an alternative embodiment could leave out the rear surface, and simply include pleated top, bottom and side surfaces embodied in a four-sided, rather than a five-sided liner apparatus  1 . In this embodiment, the rear surface of microwave oven  5  can alternatively be protected, for example, by a separate rear surface liner sheet substantially similar to separate front door liner sheet  54 . 
     Ideally, the liner material used to construct microwave oven liner  1  should have structural integrity and be able to free-stand in the microwave device on its own, requiring minimal or no supports. This material should still be free-standing after many microwave uses, and should need to be disposed of because of the spilled food that it has prevented from being caked on the microwave surface—not due to the liner becoming deformed from heat. The ideal material should also not allow food to be absorbed or soaked into its surface, as this would cause the liner to stick to the microwave surface, defeating its purpose. 
     Therefore, materials meeting the requirements would be able to withstand repeated microwave bombardment and not become distorted from the water vapor or steam resulting from routine food preparation. High-density polyethylene, high-density polypropylene, high-density polystyrene, polycarbonates, polyethylene, polypropylene, polystyrene, and blends containing these polymers meet these requirements. These materials have a high heat distortion temperature and therefore can withstand repeated microwave bombardment and the steam that results in day-to-day food preparation. They also will not absorb food spatters into their surface. 
     It is also to be noted that many microwave ovens  5  contain lights to light their interior region, and/or fans for air circulation. It may therefor be desirable for the material used to fabricate liner  1  to have, for example, a transparent or cutout (e.g., using perforations) region  55  proximate the light location, and to have, e.g., vent regions  56  (e.g., small aperture vents) for air passage proximate any air fans. It is understood that the proper location for these light and air passages will likely vary from one microwave model to the next, due to differing placements of lights and fans on different microwave models, and that locations  55  and  56  are simply marked as an example. 
     In an alternative preferred embodiment illustrated by FIG. 6, the pleating structure is eliminated entirely, and microwave oven liner  1  comprises four distinct and separate microwave oven liner quadrant sections, as opposed to the continuous, unitary structure of FIGS. 1 through 5. In this embodiment, microwave oven liner  1  comprises an upper left quadrant  61 , an upper right quadrant  62 , a lower left quadrant  63 , and a lower right quadrant  64 . Each of these quadrants in turn comprises three surfaces which are slidably overlapped into one another as illustrated by expansion/contraction lines  66  so that the size of the overall microwave oven liner  1  formed by the combination of all four quadrants can be suitably matched to the size of microwave oven  5 . 
     In particular, liner-to-oven securing means  51  are used at suitable locations on the surface of microwave oven liner  1  to secure each quadrant to the interior of microwave oven  5  so as to achieve complete coverage of the top, bottom, side, and rear walls of microwave oven  5 . Upper left quadrant  61  comprises upper left quadrant rear  611 , top  612  and left side  613  surfaces which are respectively secured to the rear, top and left walls of microwave oven  5  toward the upper left of microwave oven  5 . Upper right quadrant  62  comprises upper right quadrant rear  621 , top  622  and right side  623  surfaces which are respectively secured to the rear, top and right walls of microwave oven  5  toward the upper right of microwave oven  5 . Lower left quadrant  63  comprises lower left quadrant rear  631 , bottom  632  and left side  633  surfaces which are respectively secured to the rear, bottom and left walls of microwave oven  5  toward the lower left of microwave oven  5 . Finally, lower right quadrant  64  comprises lower right quadrant rear  641 , bottom  642  and right side  643  surfaces which are respectively secured to the rear, bottom and right walls of microwave oven  5  toward the lower right of microwave oven  5 . 
     Once these microwave oven liner quadrant sections  61 ,  62 ,  63  and  64  have been secured to microwave oven  5 , there is some partial overlapping of these various surfaces  611 ,  612 ,  613 ,  621 ,  622 ,  623 ,  631 ,  632 ,  633 ,  641 ,  642 , and  643 , depending on the size of microwave oven  5 . In this embodiment, the rear liner surface earlier discussed in reference to expansion regions  14  and  15  comprises partially-overlapping rear quadrant surfaces  611 ,  621 ,  631 , and  641 . Microwave oven liner top surface  16  comprises partially-overlapping upper quadrant surfaces  612  and  622 . Microwave oven liner bottom surface  17  comprises partially-overlapping lower quadrant surfaces  632  and  642 . Microwave oven liner left side surface  18  comprises partially-overlapping left side quadrant surfaces  613  and  633 . Finally, microwave oven liner right said surface  19  comprises partially-overlapping right side quadrant surfaces  623  and  643 . 
     It is to be recalled that microwave oven liner  1  needs to be expandable in height between approximately 6 and 15 inches, in width between approximately 11 and 21 inches, and in depth between approximately 10 inches and 18 inches. Thus, each of these quadrants preferably has a height  11  of approximately 6 inches, a width  12  of approximately 11 inches, and a depth  13  of approximately 18 inches. To accommodate depth adjustment, the depth of these quadrants can be trimmed or folded from 18 down to 10 inches as discussed earlier in reference to the embodiments of FIGS. 1 through 5, using, for example, not limitation, the optional depth adjustment lines  106  of FIGS. 1 and 2. With an 11 inch width per quadrant, the width of microwave oven liner  1  can be varied from 11 to 22 inches depending on the degree of width overlap, thus accommodating the required width adjustment. However, the problem earlier discussed in reference to FIG. 4 regarding the need to expand the height of microwave oven liner  1  by a factor of greater than 2 to 1 still applies here. Thus, if each quadrant has a height  11  of approximately 6 inches as just stated, it will not be possible to expand the height of microwave oven liner  1  to greater than 12 inches without further accommodations. There are several options for this, as discussed below. 
     One option, as also illustrated in FIG. 6, is to provide a fifth microwave oven liner section such as the illustrated midsection height extender strip  65  comprising height extender strip rear  651 , left side  654  and right side  655  surfaces. Height extender strip  65  has a height  656  of approximately 3 or more inches, and is only needed for microwaves of greater than 12 inches in height. Height extender strip  65  is similarly attached to microwave oven  5  using liner-to-oven securing means  51 , so as to cover the gap between the upper quadrants  61 ,  62  and the lower quadrant  63 ,  64  when these are secured to a microwave oven  1  of greater than 12 inches in height. This affords protection the interior surfaces of microwave oven  5  that would otherwise be exposed between upper quadrants  61 ,  62  and the lower quadrant  63 ,  64 . For microwave ovens of less than 12 inches in height, height extender strip  65  is unnecessary. 
     Another option, illustrated in FIGS. 7 and 8, uses two distinct and separate microwave oven liner half sections. In this embodiment, microwave oven liner  1  comprises a left half  71 , and a right half  72 . Left half microwave oven liner comprises an upper left quadrant  61  and a lower left quadrant  63  similarly to FIG. 6, as well as an expandable left half vertical pleating structure  73  comprising, in this illustration, for example, not limitation, a single vertical pleat adjoining upper left quadrant  61  and lower left quadrant  63 . Right half microwave oven liner comprises an upper right quadrant  62  and a lower right quadrant  64  similarly to FIG. 6, as well as an expandable right half vertical pleating structure  74  comprising, in this illustration, for example, not limitation, a single vertical pleat adjoining upper right quadrant  62  and lower right quadrant  64 . Thus, this vertical pleating structure on the left and right sides, as well as in the rear, takes the place of height extender strip  65  so as to protect the mid-height region of microwave oven  5  and enable the greater than 2 to 1 height expansion required to accommodate microwave ovens  5  ranging in height from 6 to 15 inches. 
     Many variations from the above will certainly occur the those of ordinary skill in the art, and are considered to fall within the scope of this disclosure and its associated claims. For example, the embodiment of FIG. 6 could also be used without any of the rear surfaces  611 ,  621 ,  631 ,  641  so as to cover only the top, bottom and sides of microwave oven  5 . 
     In the fully-collapsed state of FIG. 7, microwave oven liner  1  needs to be approximately 6 inches high, while in the fully-expanded state of FIG. 8, microwave oven liner  1  needs to be approximately 15 inches high. A simple algebraic calculation reveals that if the height of the upper and lower quadrants are to chosen to be substantially equal, then the height of each quadrant should be chosen to be approximately 5.25 inches, while the length (height) of the vertical pleating structures  73  and  74  should be chosen to be approximately 4.5 inches. Thus, when fully collapsed as in FIG. 7, microwave oven liner  1  will be 6=5.25+5.25−4.5 inches high, and when fully expanded as in FIG. 8, microwave oven liner  1  will be 15=5.25+5.25+4.5 inches high. In the intermediate states, the left and right halves are expanded to the desired height, and the excess pleating may then be “scrunched” as necessary. Liner-to-oven securing means  51  is again used to secure microwave oven liner  1  to microwave oven  5 . 
     In light of the above, many other variations may also occur to someone of ordinary skill which are considered to be within the scope of this disclosure and its associated claims. For example, not limitation, the embodiment of FIG. 6 can be varied so as to eliminate the rear surfaces  611 ,  621 ,  631 , and  641 , and thus only cover the top, bottom and sides of microwave oven  5 . Then, a separate liner can be applied directly to the rear of microwave oven  5 . 
     Another variation, for example, not limitation, is for left half vertical pleating structure  73  and right half vertical pleating structure  74  to comprise a plurality of vertical pleats, for example, in an accordion-like structure, or, for example, in the side pleating structures earlier shown and described in connection with the embodiment of FIGS. 1 through 5. 
     A third preferred embodiment, for example, not limitation, illustrated in FIG. 9, is for all four quadrants of microwave oven liner  1  to comprise a continuous, unitary structure as in the embodiment of FIGS. 1 through 5, but using only a single pleat for expansion as in FIGS. 7 and 8. Once the vertical pleats are provided similarly to FIGS. 7 and 8, a horizontal pleating structure such as but not limited to a single horizontal pleat similar to single vertical pleats  73  and  74  can be introduced between the pleated left half  71  and the pleated right half  72 . To cover the full width range from 11 to 21 inches, the horizontal pleat is optimally selected to be about 5 inches, while the horizontal width of each quadrant is selected to be about 8 inches. Then, when fully collapsed along its width, the width of microwave oven liner  1  will measure approximately 11=8 +8−5 inches, and when fully expanded along its width, the width of microwave oven liner  1  will measure approximately 11=8 +8+5 inches. In this embodiment, the vertical and horizontal expansion pleats will intersect each other at a center intersection region  9  (shaded) of the liner rear surface in a plus sign (+) configuration, but the earlier-described pyramid is eliminated. In FIG. 9, which is drawn substantially to scale, microwave oven liner  1  is fully collapsed, is 6 inches high by 11 inches wide, has a single vertical pleat which is 4.5 inches high, and has a single horizontal pleat which is 5 inches wide. There is 0.75 inches of unpleated height above and below the vertical pleat, and there is 3 inches of unpleated width to the left and right of the horizontal pleat. FIG. 9 is a schematic illustration insofar as it illustrates the pleating regions, but does not show the pleats themselves. 
     Another variation, for example, not limitation, is to provide the microwave oven liner of FIGS. 7,  8 , and/or  9  with a plurality pleat structure such as an accordion-like pleat structure, or a similar type of pleating structure that would be obvious to someone of ordinary skill, rather than the single pleat structure discussed above. The vertical and horizontal expansion pleats will still intersect each other in a plus sign (+) configuration in the shade region  9 , but the height and width of the pleating regions will vary depending on the particular plurality pleating structures that are chosen. 
     In all embodiments, the calculations to determine the appropriate height and width for each quadrant, as well as the for the pleating structures, will of course depend upon the particular pleating structure being employed. But it is understood that this should be a simple and obvious calculation that, in light of this disclosure, and within the scope of the associated claims, can easily be performed by someone of ordinary skill. 
     While only certain preferred features of the invention have been illustrated and described, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.