Recycled Polyester is made of post industrial waste (PIR) along with post-consumer waste (PCR).  PIR is mostly from fiber plants and, to some degree, textile mill fiber waste that use to go into landfills. 

Poly ethylene terephthalate (or simply PET) is the most common polyester used for fiber purposes. This is the polymer used for making soft drink bottles. Recycling PET by re-melting it and extruding it as a new fiber saves raw materials while reducing energy consumption. Recycled polyesters are popular because they are more fire-retardant, easy to clean, and inexpensive. They can be blended with almost any other fiber. One square yard of fabric contains roughly five clear, 2-liter soda bottles.

For every pound of yarn produced from recycled polyester, 61,000 BTUs are conserved, equivalent to .5 gallons of gasoline.