This question has been coming up lately, so why not talk about it in a blog? It's not difficult to get, it's just never explained.
rPET stands for recycled PET, the bottles that we are all familiar with used for water and soda. The recycle symbol #1. PET is Polyethylene terephthalate, a member of the polyester family, which most people don't realize. What has always been the case is that PET is the same chemistry as polyester. The difference is that a PET bottle is molded and polyester is a fiber. So in most respects PET and Polyester are synonymous. If that doesn't quite add up, you could think of dough in a loaf pan to make bread or dough in a pasta machine to make linguini. The source of both is dough, but, the result is totally different.
When anyone puts a bottle in the recycle bin, it may go back through the recycle process to become a bottle, or it may become a polyester fiber of some kind. It may come back all kinds of forms. Polyester is tremendously strong, inherently water resistant, and pretty much totally color fast. In outerwear you'll find polyester as polar fleece, in general apparel because it is lightweight and wrinkle resistant, as a component in clothing (cotton/poly blend), bedspreads, sheets, curtains and in all types household fabrics. Additionally, polyester is found in tires, ropes, conveyor belts, safety belts and lots of industrial applications.
Any one of these applications could have rPET origins, but, most don't. What makes rPET fascinating is how much energy is saved in production and of course, it consumes what would otherwise go to landfill, the bottle. So when you see something labeled as rPET, rest assured that it is a recycled material.