|What is polyester and how does it work insulating clothing? — PGF, Seabrook, SC
Polyesters are a class of polymers, extremely long molecules that are commonly known as plastics. Each polyester molecule is several thousand atoms long, so that a polyester fiber resembles a tiny rope made of microscopic spaghetti strands that are all entangled with one another. Like most electric insulators, polyester plastic is a poor conductor of heat. But in clothing its main insulating effect is to trap air. While air is a terrible conductor of heat, it tends to undergo convection and convection allows it to transport heat pretty effectively. However, when air is trapped by countless tiny fibers, convection is inhibited and the air becomes a great insulator. That's why polyester fibers are such good thermal insulation—they trap air and let the air act as the real insulation.