Made from responsibly-sourced, high-quality Merino wool, the 100% Merino Wool MummyLiner is soft, lightweight, and stretchy, making it ideal for use in a variety of different conditions. The natural hollow spaces in the wool allow air to circulate, making it excellent at regulating temperature. Plus, it adds an impressive 12.6 ℉ of temperature to your sleeping bag, ensuring you stay warm and comfortable all night long.