Helsport's liners comes in two versions. Rectangular for use with a duvet and pillow, and fitted for sleeping bags. The fitted/mummy liner is used in sleeping bags to postpone the need for cleaning, thus prolonging the life of the bag. The Rectangular liner can be used alone or together with a duvet and pillow on cabin trips, camping or travel. Using a liner increases comfort and hygiene, and makes the sleeping bag feel warmer.