Down

Down is an unsurpassed fill for sleeping bags in a number of ways. High-quality down provides the best thermal insulation relative to its weight and volume. Fluffy down is very breathable and it can absorb body vapor. How much warmth down provides per gram is expressed in fillpower (FP). From 650 FP you have high-quality duck down, from 750FP high-quality goose down. Down does lose insulation value when it gets wet.