The Sea to Summit Thermolite Reactor Extreme Liner increases sleeping bag performance by up to 15 deg C with its super insulating 110g/m sup 2 Thermolite reg fabric The spacious design is slightly tapered from head to foot to reduce weight & increase thermal efficiency & the drawcord hood can be cinched down for extra warmth when required This knit fabric also has serious stretch to it making the Reactor Extreme the ideal liner for the restless sleeper