Also read posting by Steve Baggett
The following comes from the usenet form rec.photo.darkroom (http://www.photodigital.net/lists/rec.photo.darkroom/subject.html):
I found a table of O2 permeability of various packaging films for food storage. There are similar results, plus some additional materials. They are in the same units shown above:
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Low Density Polyethylene (LDPE): 510 (food wrap, grocery bags) Orientated Polystyrene (OPS): 355 (Styrofoam) Polycarbonate (PC): 300 (eg Lexan) High Density Polyethylene (HDPE): 185 (Milk, juice jugs) Oreintated Polypropylene (OPP): 160 (Margarine tubs) Polyvinylchloride (PVC): 8 (Cleanser bottles) Polyethylene Terephthalate (PET): 6 (Soft drink bottles) Polyvinyldichloride (PVdC): 0.6 (Saran wrap) Ethylene Vinyl alcohol copolymer (EVAC): 0.1 (interior coatings, gasoline containers)
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And here is a list of the recycle codes printed within the recyclable triangle on the bottom of most containers:
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Code 1 PET (Polyethylene/Terephthalate) usually a clear plastic - includes soft drink and beverage bottles
Code 2 HDPE High Density Polyethylene includes milk jugs, detergent, bleach, some water and vinegar containers and plastic bags
Code 3 PVC Polyvinyl Chloride includes some water containers, cooking oil, glass cleaner and liquid wax bottles (usually clear)
Code 4 LDPE Low Density Polyethylene includes plastic bags, bread bags and food wrap
Code 5 PP Polypropylene includes some yogurt and margarine containers, shampoo and syrup bottles
Code 6 PS Polystyrene includes disposable hot and cold drink cups, plastic plates and utensils, fast food clamshells, egg cartons and meat trays
Code 7 OTHER other resins, complex composites and laminates such as drink boxes and squeezable ketchup bottles