http://www.bagssleeping.us - Down-the filamentous and fluffy layer underneath the feathers. Positives: All being equal down is warmer, lighter, more comfortable, compresses smaller, and can last a lifetime if cared for properly. Goose down is the standard others are compared to. The more it lofts the better it insulates. This is known as fill-power, the higher the number the better it retains heat.
