A heat set polypropylene rug is one in which the yarn is processed to produce soft fibers that are resistant to wear and tear and repel stains. This type of rug is antistatic, which makes vacuuming easier because animal hairs and lint don't easily adhere to the fibers.
Weave density and yarn width define the quality of heat set rugs. When the yarn width is fine, more tufts are required to create the rug and results in the weave being made thicker and more durable. Heat set polypropylene rugs are available in both plush and twist piles. The advantages to twist pile rugs over plush are their resistance to flattening and their longevity.