Trademarked by the Invista corporation, Thermolite is a synthetic down insulation. Used in outerwear, socks, sleeping bags and other items, Thermolite was designed to emulate the softness of down feathers but improve upon their insulating properties at a reduced cost. Items made with Thermolite tend to be less bulky, warmer overall and better at wicking away moisture than similar items made with down feathers.
Thermolite, like all synthetic insulation, is made of fine polyester filaments spun in a way that creates pockets of air between each fiber to emulate the way that soft down feathers create pockets of warm air to keep birds warm even while wet.
Thermolite in particular uses a unique hollow-fiber design that allows the insulation to trap air inside as well as in between each fiber, enabling the insulation to dry faster while also making the items that use it warmer. This design also makes it significantly lighter than some other forms of synthetic insulation, allowing jackets and other outerwear to be layered to maximize the warmth and comfort of the wearer.
