In outdoors, the main heat preservation function is provided by the sleeping bag. Depending on the filler materials, there are mainly two kinds of sleeping bags: fiber cotton sleeping bags and down sleepingbags. While, according to the design, the styles contain envelope form and mummy form. Among all sorts of sleeping bags, consumers need to choose the temperature in the first place. In general, the sleeping bag has three indicators: the lowest temperature, comfortable temperature, and the highest temperature. It is very deangerous to select a sleeping bag whose environment temperature is blow the specified temperature. Even in summer, people also had better choose sleeping bags that can resist - 10 ℃ low temperature.