The soft and cozy Synergy Sleeping Bag Liner adds warmth, comfort and years of life to any sleeping bag. Contributing up to 5F/3C degrees of warmth to your sleeping system, the soft, stretch-knit polyester also serves as a protective barrier to your expensive sleeping bag's materials, absorbing the sweat and oils that would otherwise go directly into your bag and decrease its loft. Now, instead of washing and drying your entire bag or allowing that grime to clump up the insulation, all you have to do is remove the liner and toss it in the washing machine.