thermolite Imported Insulated sleeping bag liner adds extra warmth and personal hygiene to any sleeping bag. Thermolite Pro technology using knitted, hollow-core fibers and absorbing infrared ceramic pigments to reflect your body's heat back to the wearer for enhanced warmth and comfort Drawcord footbox can be opened or closed for optimal comfort and integrates perfectly with the footbox of our Free-Flow Zip system in select Sea to Summit sleeping bags HeiQ Fresh odor control technology helps keep the liner fresh even after extended use Knitted fabric provides incredible stretch and freedom of movement in this mummy-shaped liner and works seamlessly with sleeping bags of any shape, Sea to Summit Guarantee is offered for the Lifetime of this product Sea to Summit Reactor series insulated sleeping bag liners can extend the comfort range and improve personal hygiene of any sleeping bag. Thermolite hollow core fibers are constructed like the fur of a polar bear, efficiently trapping heat and providing a luxuriously soft, comfortable feel. The stretch-knit fabric provides optimal comfort, and ensures the Reactor fits any sleeping bag. Additionally, the drawcord footbox offers plenty of ventilation and the versatility of walking around camp while still wearing your liner. Available in three different weights, Reactor technical liners make your existing sleeping bag warmer and more versatile. The Regular Liner uses hollow-core Thermolite Pro fabric with infra red-absorbing ceramic pigments and Thermolite EcoMade fibers. This lightweight fabric adds up to 14F of warmth to your sleep system. The Extreme Liner features a thicker hollow-core Thermolite Pro fabric to add up to 25F of warmth to your sleep system. The Fleece Liner employs hollow-core Thermolite Pro fibers in a grid-pattern to deliver our warmest sleeping bag liner which adds up to 32F of warmth to your sleep system.