24 are preferably pvc but one or both may alternatively be other polymer films including but not limited to amorphous pet apet petg a rubber modified nitrile polymer such as barex u00ae a registered trademark of bp chemicals inc polypropylene or polystyrene each of these alternatives has different desirable properties for example where gamma sterilization is required such as in the medical device industry a petg film can be used since pvc cannot be so sterilized without being degraded and yellowed if an additional oxygen barrier is required which occurs commonly in the food packaging industry for purposes of flavor protection of meats and cheeses land sometimes in the pharmaceutical industry a rubber modified nitrile polymer film such as barex u00ae can be employed since it provides an additional oxygen barrier to the product along with the moisture barrier otherwise provided by product 22 in some cases a halogen free contact surface is required in these instances the use of polypropylene or polystyrene is appropriate polymer films 18 and 24 are preferably each approximately 5 0 mils thick although different thicknesses in the range of approximately 0 5 mils to 15 mils may be used furthermore laminated layer 4 may be either symmetrical or asymmetrical in structure such that polymer films 18 and 24 may be comprised of the same or of different materials and may have the same or different thicknesses for example polymer film 18 could be 5 0 mils thick and be comprised of pvc while polymer film 24 could be 7 5 mils thick and comprised of petg product 22 is preferably a fluoro polymer based.