The THERMOLITE® Reactor Compact sleeping bag liner is the ideal choice for gram counters under six feet who want to add warmth to their sleep system. The world’s first ‘hybrid’ sleeping bag liner uses a combination of two weights of THERMOLITE® fabric, with the warmer fabric strategically positioned across the torso and in the footbox. The THERMOLITE® fibers work like the hollow structure of a polar bear s fur, which traps extra insulating air. The Reactor Compact Plus keeps your sleeping bag clean, plus it s super easy to wash.