As anyone who has ever used a sleeping bag realizes, the primary purpose of these bags is to provide warmth and insulation. They serve as bedding when more standardized bedding is not available. Prime examples of these times would be while camping, hiking, or otherwise trekking. A sleeping bag is almost always used in conjunction with a sleeping pad or a tent.
If a tent isn’t feasible, some people opt for a bivouac sack. These are waterproof covers that cover sleeping bags. Sleeping bags are almost always outfitted with zippers on the side. This is true whether it’s a standard straight bag or a tapered mummy bag. Most campers prefer these mummy bags, because they increase heat retention. But they also have less surface area and volume, so they fold up more compactly than other bags.