Some polyester fibers are stretchy.
The stretchiness of a polyester garment depends on the fibers that were used to create the fabric. A variety of materials can be used to create polyester fibers each having variable properties that add to the garment's durability and ease of care.
FTC Defines New Stretchy Polyester Fiber
The Federal Trade Commission has implemented guidelines for manufacturers in terms of labeling products for resale and has recently added the new term elasterell-p to be used to describe a polyester fiber that if stretched will rapidly revert to its unstretched length. As would follow, garments made with this polyester fiber are very stretchy. You can find elasterell-p in stretchy jeans, blouses, sweatshirts, and a variety of other popular garments.
How Polyester Is Manufactured
The building blocks of synthetic polyester fibers are acids and alcohols derived from petroleum. Placing the acids and alcohols together with an antimony catalyst causes a reaction to occur. To form fibers the reaction must be carried out and high temperatures and vacuum conditions. Once the fiber ribbons that are created are cooled, they are cut into chips and melt spun. Melt spinning means that the material is melted and then pushed through a spinneret (similar to a pasta machine). When the fibers hit the air, they are immediately solidified.