The temperature in the sleeping bag can be raised using a liner. Since you won't be perspiring heavily within the sleeping bag – which would otherwise cause the down to become damp – you will also be able to take better care of the bag. A liner can also be cleaned more easily. Our liner has an arm opening so you can combine it with our sleeping bags with arm openings. It also gives the arms more space inside the sleeping bag and helps keep the liner in place. It has a head cover that can cover your eyes if you need the darkness to overwhelm you. This model uses the same fabric that we use as the lining for our Explorer Pro sleeping bags.