To assist recycling, the Plastic Bottle Institute of the Society of the Plastics Industry (SPI) devised the system to mark plastic bottles by type. You'll see a triangle with three "chasing arrows" encasing a number corresponding to the plastic type: PETE, HDPE, PVC, LDPE, PP, PS, and OTHER.

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promo_three_prong SPE - Society of Plastics Engineers SPI - The Plastics Industry Trade Association

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