It is important to sleep in a room not too hot nor too cold. For optimal comfort, the duvet should be 30cm longer than your height and at least 30cm wider than your bust. Double size duvets should at least be the same size with as your bed.Fill Power is an expression of the down's insulating ability and quality. The higher the fill power the better the quality. Thus, it's better to get duvets with small amount of down with a high fill power, which warms better, than duvets with large amount of filling with a low fill power.