Wool

Wool is a good option as a filling for a sleeping bag. Wool can absorb up to 30% of its own weight in moisture and still retain its insulating properties. The moisture that wool absorbs passes on in small amounts to the outside of the bag, preventing cooling by evaporation. During the night, the body releases moisture, up to 500 ml. When absorbing and releasing this, wool balances the sleeping climate inside the sleeping bag, promoting a restful night's sleep.