The plastic types were defined by the Society of the Plastics Industry (SPI):

    * Type 1 - PETE  Polyethylene Terephthalate (PET)
                     Soda & water containers, some waterproof packaging.
    * Type 2 - HDPE  High-Density Polyethylene
                     Milk, detergent & oil bottles.  Toys and plastic bags.
    * Type 3 - V     Vinyl/Polyvinyl Chloride (PVC) 
                     Food wrap, vegetable oil bottles, blister packages.
    * Type 4 - LDPE  Low-Density Polyethylene
                     Many plastic bags.  Shrink wrap, garment bags.        
    * Type 5 - PP    Polypropylene
                     Refrigerated containers, some bags, most bottle tops,
                     some carpets, some food wrap.
    * Type 6 - PS    Polystyrene
                     Throwaway utensils, meat packing, protective packing.
    * Type 7 - OTHER Usually layered or mixed plastic.
                     No recycling potential - must be landfilled.

Types 1 and 2 are commonly recycled. Type 4 is less commonly recycled. The other types are generally not recycled, except perhaps in small test programs. Common plastics polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) do not have recycling numbers.

The code must be molded into the plastic item. The symbol should be easily visible for sorting purposes. The best symbols are large with a different surface finish than the surrounding plastic. If the container has a matte surface (rough), then the symbol should be smooth, a smooth container should have a rough recycling symbol.

Understand that plastic recycling is really in infancy. The process is messy and inefficient. Numerous problems exist. For example plastic from a "blow mold" (the neck of the bottle is narrower than the body) has a slightly different structure from the exact same plastic used in an "injection mold" (where the opening is the widest part of the product). Because of low processing temperatures plastic is highly vulnerable to contamination by food, labels and different plastics.

Much recycled plastic ends up as low grade plastic lumber. Valid HTML 4.0!