The Reactor Fleece Liner built from hollow-core Thermolite® Pro fibers used in a grid-pattern to deliver our warmest sleeping bag liner and the core of any quality cold weather sleep system. You can regulate your temperature using the shoulder zippers and drawcord footbox, which also align perfectly with the Free Flow-Zip system of Sea to Summit sleeping bags. The versatile Reactor Fleece Liner delivers comfort across multiple seasons or can even be used as a stand-alone sleeping bag in warm weather. Additionally, the drawcord footbox offers plenty of ventilation and the versatility of walking around camp while still wearing your liner if needed.