Therm-A-Rest Synergy Sleeping Bag Liner is a perfect sleeping bag to add comfort, warmth and protection to any sleeping bag, or to spend the nights in a shelter or tent when it's particularly hot. Made from soft and comfortable stretch polyester, it also acts as a protective barrier to your sleeping bag materials and helps add up to 3 ° C of warmth. Furthermore, using Synergy as a lining at the end of each excursion, you can just throw it in the washing machine without having to worry about the entire sleeping bag. Therm-A-Rest Synergy Sleeping Bag Liner