The sea to summit thermolite reactor sleeping bag liner is a versatile lightweight mummy shaped liner with drawcord hood that can either be used on its own in warmer weather or combine with your sleeping bag to add up to 8 c of warmth in cooler conditions thermolite fabric is soft to touch yet lighter weight and more packable than fleece material it is a hollow core fibre that provides amazing warmth for tis weight and remains extremely breathable making it an excellent choice for a sleeping bag