The new Optimus sleep system is designed to keep outdoor adventurers comfortable in fluctuating weather conditions from 0°F up to 25°F with just one sleep system. The all-in-one, transformable sleep system is uniquely designed to deliver high-end performance without adding unwanted bulk and weight to your backpack. The Optimus system consists of two mummy-shaped sleeping bags, a bivy shelter and a compression stuff sack that holds all the components. When all three components are used together, you get the maximumamount of insulation and protection from the system, all the way down to 0°F. Both bags are filled with Thermolite insulation for superior warmth and have polyester diamond ripstop shells to resist wind, water and the elements. The bivy is made with Breath Easy ripstop waterproof fabric that also has a breathable polyurethane coating. Welded seams protect you from all types of weather.