Sleeping bags are usually rated for the lowest temperature at which they can keep a person comfortable. The amount and type of insulation achieve the rating. The ratings are a general guide, not a rule. Sleeping bags provide lightweight sleeping options for all types of warm and cold weather. Different insulating materials are available: synthetic fill or down. A basic sleeping bag is a square blanket fitted with a zipper on one or two sides - if you are camping in a place with warm weather this is the type of sleeping bag you need. This bag is roomier and absorbs more body heat. The second major type is called a mummy bag because of its shape. A Mummy Bag is made to confine warm air on your head as it provides a hood ensuring that heat will not escape. It takes on body shape and that is why it maintains heat better than rectangular sleeping bags. Choose from many different models and colors.