The Logic Behind Sleeping Bags A sleeping bag should do two things: \r\n1) Keep you warm.\r\n2) Keep you dry. \r\n\r\nA sleeping bag’s job is to help you sleep comfortably and protect your body from the elements. When choosing a sleeping bag, be sure to consider elevation, temperature, climate and terrain, as well as your sleeping preferences.\r\n\r\nThe two primary considerations when choosing a bag are insulation type and temperature rating. Let’s start with the two main insulation types: synthetic and down. \r\nSynthetic Insulation consists of very fine, tightly woven fibers that form small air pockets to trap body heat. They dry quickly and stay warm when wet. Synthetic insulation is best in a wide range of conditions, as synthetic fibers will not absorb moisture.\r\nDown Insulation is a natural insulation and the most packable of the insulation types. Goose or duck down plumes provide warmth by trapping body heat within the space between down clusters that insulate the garment. Down is best in cold climates and where less weight is optimal, as the warmth-to-weight ratio is the highest. Note: There are new treatments that some manufacturers use that prevent the down clusters from collapsing when wet, therefore helping them maintain warmth even in the presence of moisture.