These are the seven categories of Plastic Packaging Resins as defined by the Society of the Plastics Industry, Inc. (SPI)

(Listed in order of recycling code)

  1. PETE - Polyethylene Terephthalate (commonly known as Polyester is a clear, rather tough plastic that serves as a fairly good barrier to gas and moisture, and can stand up to reasonably high temperatures. As a result, it is commonly found in food containers. Most notably, soft drink and water bottles, as well as in frozen dinner trays that can tolerate oven temperatures other packaging resins may not survive. It is also used in the naff, but startlingly similarly shaped bottles used for mouthwash and salad dressing. PETE is very highly recycled, as it has many high-demand uses. Used commonly in carpets and furniture as yarn and fiberfill, this plastic has made a large impact in recent years as Polartec fleece.
  2. HDPE - High Density Polyethylene is a gas permeable plastic that is stiff, inexpensive, and resistant to a wide variety of chemicals and moisture. In the absence of dyes, HDPE is translucent, making it a useful plastic for showcasing food items, but its gas permeability limits its uses to products with a relatively short shelf life (an argument for those of you who say that glass makes a better container for milk than does plastic, as glass is not gas permeable). Milk, yogurt and juice containers are commonly made from HDPE. The bags that line cereal boxes and bags used in stores are commonly made from HDPE. As HDPE is stable in the presence of a wide variety of chemicals, it is used regularly for household cleanser containers. When recycled, HDPE is remarkably reusable, frequenting many of the containers from which it is recycled, from vitamin bottles to laundry detergent bottles. HDPE has also found its way into artificial lumber and structures (dog houses, Little Tikes jungle gyms, etc...)
  3. V - Polyvinyl Chloride (PVC or Vinyl) - Vinyl is exceptionally versatile, and it retains its strength, even when made flexible. Because it is tough and stable when exposed to electrical current, flexible vinyl is used very commonly for wire insulation (anyone reading this on a computer probably owes flexible vinyl a great deal). Medical tubing, blood bags, and leather clones are also made from flexible vinyl, the latter giving vinyl a bad name. It is important to note that vinyl is clear but commonly dyed (and opaque) when used in cloth applications. When rigid, vinyl's resistance to grease, oil and many other classes of chemicals makes it an ideal plastic for construction. Rigid vinyl is used regularly in siding, windows, pipes, fittings and flooring. Recycled vinyl is used for flooring, road gutters, packaging and, pimp this, speed bumps.
  4. LDPE - Low Density Polyethylene - LDPE is fairly tough and transparent, but is not very resistant to heat. LDPE is used most commonly in film applications (applications that use a normally rigid, but thin layer of plastic in a way that cloth might be used). LDPE is used in bread bags, frozen food bags, and squeezable bottles. It is also very popular in heat sealing applications, as it is effected quickly when modest amounts of heat are applied (Shrinkwrap). LDPE is recycled fairly regularly, and makes its way into trash bags, compost bins, trash cans, floor tile, shipping envelopes and molded furniture.
  5. PP - Polypropylene - Polypropylene has exceptional resistance to chemicals and bears the lowest density of the plastics commonly used in packaging. It has a relatively high melting point, making it an ideal plastic for hot-fill liquids. Polypropylene is widely used for everything from medicine bottles to molded automobile parts to the very ketchup bottle that you might be drinking from right now. Recycled polypropylene regularly serves in ice scrapers, brooms, brushes, lunch trays and plastic-tined rakes.
  6. PS - Polystyrene - Polystyrene is a more commonly known as Styrofoam, only one of its possible forms. Styrofoam is (rather obviously) a foamed version of polystyrene that is used very commonly in food packaging. Styrofoam makes its way into cups, egg cartons, plates and peanuts on a fairly regular basis. In spite of its acceptance as a container for prepared food and beverages, polystyrene has a melting temperature low enough melt in hot cooking oil. Rigid polystyrene is used in rulers, compact disc cases (jewel cases), clear medicine bottles and light switches/plates. Polystyrene is easily recycled into many of the items from which it is recycled and a few others, including, packaging materials, foam insulation, thermometers and food containers.
  7. OTHER - As the field of plastics is a constantly expanding one, SPI took note of the possibility that a plastic packaging resin might be used that did not fit into one of the six categories listed above, and acted accordingly, adding a default group, OTHER.

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