A duvet insert is meant to be draped over your bed, covering you just like a comforter. While some duvet inserts are filled with synthetic materials such as polyester, Savvy Rest duvet inserts are filled with wool and covered in organic cotton. Wool is an incredible natural fiber because of its ability to wick away moisture and keep you cool during the warmer months and warm during the colder months. It’s very breathable and helps regulate temperature, unlike synthetics.