Slumberdown's microfibre 4.5 tog duvet cleverly regulates your temperature so you don't get too hot or too cold through the night. Dacron hollow fibber is formulated to carry excess heat and moisture away from your head and body into the surrounding. The more heat that you generate the harder it will work to keep you cool. But if you're already cool it will slow right down so you don't get too cold either. It gently wraps around your contours so it stays with you as you move in the night. It is also lightweight even at high tog counts.