The Society of the Plastics Industry, Inc. (SPI) introduced its resin identification coding system in 1988 as a means of helping recyclers identify the resin content of bottles and rigid containers commonly found in the residential waste stream.

The presence of the coding symbol on the plastic product does not indicate that the product is recyclable or recycled locally.

	Polyethylene Terephthalate (PETE): PETE is commonly used in carbonated beverage containers because of its excellent ability to keep the "fizz" in the beverage. PET is also used in food and other beverage containers because it is clear (so the contents can be seen) and resists breakage.
	High Density Polyethylene (HDPE): HDPE's ease of processing makes it suitable for use in manufacturing large 4-litre containers, such as bottles for milk, juice and water. It is also used for packaging ice cream because it can withstand cold temperatures without becoming brittle. In addition, HDPE bottles are chemically resilient, making them suitable for laundry products, such as detergent and bleach. HDPE also offers great strength in very flexible applications, like grocery bags.
	Vinyl (V) or Polyvinyl Chloride (PVC): Vinyl containers and film, manufactured from PVC resins are not widely used in consumer packaging; however, they are used for some jars and bottles as well as meat wraps. Vinyl is used to make transparent bottles that have handles because the material has good flow characteristics and the handle can be molded easily right into the bottle.
	Low Density Polyethylene (LDPE): This plastic is used in some squeezable bottles and in lids for tubs because if its flexibility. It is also used in film applications not requiring sophisticated barrier properties.
	Polypropylene (PP): Polypropylene is used primarily in tubs, like those used for yogurt or margarine, because it is resilient to high temperatures and can accommodate hotfill liquids (i.e. when the margarine is poured into the tub, it is in a hot, liquid state). PP in its tub application is stiff allowing for a thinner wall which makes it an efficient packaging material.
	Polystyrene (PS): Polystyrene is typically used as a protective plastic and can appear in either a foamed state (like meat trays) or in a clear, transparent state (like take-out bakery or deli-meat containers). Polystyrene does not absorb excess fluids (thus its use in meat trays) and is also a good insulator (making sure your coffee or soup stays hot).
	'Other' Plastics: Code 7 is a catch-all for many different types of plastics. This code identifies a variety of plastics which are not in the first six categories. Code 7 can be a mixture or layers of different plastics which provide unique properties such as extending the shelf life of products.