A great option for those wanting extra warmth whilst they sleep. A sleeping bag liner will help prevent the inside of your sleeping bag from dirt and they're easily washable, extremely lightweight and packable. We stock silk and cotton liners at Penrose Outdoors. Cotton is a natural fibre so it delivers warmth and gives fantastic comfort against the skin. Although they are slightly more expensive, silk liners weigh significantly less than cotton liners and they tend to pack down into a smaller size.