Last modified on May 28, 2018, at 17:24

Resin identification codes

An example of a resin identification symbol, for the common PETE plastic

Resin identification codes, also known as "SPI codes"[1] are symbols identifying the type of plastic an item is made of. They were created in 1988 by the Society of the Plastics Industry, Inc to make the recycling of plastics easier.[2]

The symbol consists of the triangular recycling symbol with a number and acronym in the middle. There are seven symbols, using the numbers one through seven.

The symbols are:

  • 1- PETE: Used primarily in bottles, for products such as water, juice, ketchup, and others
  • 2- HDPE: Used for milk containers, detergent bottles, etc.
  • 3- PVC: Best known for its use in PVC piping, and difficult to recycle
  • 4- LDPE: Used largely where flexibility is necessary- plastic containers, plastic shopping bags, etc.
  • 5- PP: Also used in containers, such as for yogurt and at deli counters
  • 6- PS: Used primarily in foam packaging and insulation. Styrofoam is made from it
  • 7- Other: This is not a specific plastic, but a mix of the above, or a different kind not included in the identification codes. "Other" plastics are used in some large juice containers and reusable containers, and in "plastic lumber."[3]

Other Uses

In addition to materials handling such as fabrication, repair and working[4], SPI codes should be used with caution because their purpose is to support recycling facilities.

Maintenance, Repair and Fabrication SPI codes are useful for repair purposes because of differences between the use of adhesives, solvent bonding, and thermal bonding vary between plastic types.[4]

Microwave Safety SPI codes do not indicate that a given container is safe for microwave use[5], as only the base polymer is indicated by the code. While some plastic types are generally unsafe for microwave heating,[6] most references recommend avoiding the use of any plastic containers for microwave cooking,[6][5] with occasional reports of containers labelled "microwave save" showing evidence of having reacted into food.


  1. [1]
  4. 4.0 4.1 3M article on plastic adhesives
  5. 5.0 5.1 Microwave Safe Plastics
  6. 6.0 6.1 - What Are the Numbers That Say That Plastic Is Safe to Use in the Microwave Oven?