Fine yarn and a special weaving technique make our high quality cotton a very lightweight and durable fabric. It is breathable, very comfortable against your skin and creates a natural vapor balance. Cotton is machine washable and colorfast. Cocoon Mummy Liners are tapered sleeping bag liners to add warmth and comfort to any mummy bag. Easy to wash, MummyLiners extend the life of your bag by protecting it from dirt and body oils.