Down-filled bags are lighter, and mummy-style bags insulate most effectively and are your best choice for colder, high-elevation conditions. Most sleeping bags have a temperature or comfort rating, which indicates the lowest temperature that the bag is designed to accommodate. For the Inca Trail, we recommend a 3-season bag, which has a temperature rating of 10-35° Fahrenheit. If you don't want to bring your own sleeping bag, you can rent a 3-season sleeping bag in Cusco for +/- $12.