There’s little room for movement while sleeping in this bag, and some people dislike the uncomfortable entombed feeling. However, mummy sleeping bags are form-fitting for a purpose, especially at freezing temperatures. This shape effectively eliminates the spaces between you and the bag to keep you warm. It also lessens the weight of the gear, making it easier to carry. There are more spacious rectangular sleeping bags that you can bring to extreme conditions. But they tend to be too heavy and bulky for long-distance treks and back-country camping.