Plastic Identification Codes

You’ve probably noticed on most plastic products a recycling symbol with 1, 2, 3, 4, 5, 6 or 7 along with letters. So what are these exactly? The SPI resin identification coding system is a set of symbols placed on plastics to identify the polymer type. The symbols used in the code consist of arrows that cycle clockwise to form a rounded triangle and enclosing a number, often with an acronym representing the plastic below the triangle. When the number is omitted, the symbol is known as the universal Recycling Symbol, indicating generic recyclable materials. Let’s take a look at the 7 plastic identification codes.

Plastic Identification Code Type of plastic polymer Properties Common Packaging Applications Glass Transitionand Melting Temperatures (°C) Young’s Modulus (GPa)
Polyethylene terephthalate(PET, PETE) Clarity, strength, toughness, barrier to gas and moisture. Soft drink, water and salad dressing bottles; peanut butter and jam jars Tm = 250; Tg = 76 2-2.7
High-density polyethylene(HDPE) Stiffness, strength, toughness, resistance to moisture, permeability to gas. Water pipes, hula hoop rings, five gallon buckets, milk, juice and water bottles; grocery bags, some shampoo / toiletry bottles Tm = 130; Tg = -125 0.8
Polyvinyl chloride(PVC) Versatility, ease of blending, strength, toughness. Blister packaging for non-food items; cling films for non-food use. Not used for food packaging as the plasticisers needed to make natively rigid PVC flexible are usually toxic. Non-packaging uses are electrical cable insulation; rigid piping; vinyl records. Tm = 240; Tg = 85 2.4-4.1
Low-density polyethylene(LDPE) Ease of processing, strength, toughness, flexibility, ease of sealing, barrier to moisture. Frozen food bags; squeezable bottles, e.g. honey, mustard; cling films; flexible container lids. Tm = 120; Tg = -125 0.17-0.28
Polypropylene(PP) Strength, toughness, resistance to heat, chemicals, grease and oil, versatile, barrier to moisture. Reusable microwaveable ware; kitchenware; yogurt containers; margarine tubs; microwaveable disposable take-away containers; disposable cups; plates. Tm = 173; Tg = -10 1.5-2
Polystyrene(PS) Versatility, clarity, easily formed Egg cartons; packing peanuts; disposable cups, plates, trays and cutlery; disposable take-away containers; Tm = 240 (only isotactic); Tg = 100 (atactic and isotactic) 3-3.5
Other (oftenpolycarbonateor ABS) Dependent on polymers or combination of polymers Beverage bottles; baby milk bottles. Non-packaging uses for polycarbonate: compact discs; “unbreakable” glazing; electronic apparatus housings; lenses including sunglasses, prescription glasses, automotive headlamps, riot shields, instrument panels; Polycarbonate:Tg = 145; Tm = 225 Polycarbonate: 2.6; ABS plastics: 2.3


When recycling plastic:

  • Rinse and sort your plastic containers by number. Recyclable plastic often must be separated by number in order to avoid contamination as it begins the recycling process.
  • Recycle type 1 (PETE) and type 2 (HDPE) plastic containers at your curb.
  • Drop off plastic grocery bags – usually type 4 (LDPE), sometimes type 2, though not always marked – at your grocery store to be recycled.
  • Most recycling programs do not recycle types 3, 5 and 7. While some of these are recyclable, the plastics industry is still in the early stages of recycling and does not recycle these in most cities unless it is through a test program.
  • For type 6, call the Alliance of Foam Packaging Recyclers, (410) 451-8340, or look at the expanded polystyrene (EPS) packaging drop off locations to find the nearest type 6 drop off center to you.
  • Take caps and pump spray tops off of plastic containers unless they are marked with a number. They are often made from a type of plastic that is different from the main part of the container and generally are not recyclable.