The Logic Behind Insulation Insulated clothing is the best way to manage the cold and your comfort in the mountains. Climbing efficiently is directly related to how hot or cold your body is running. There are many types of insulation and apparel that work well at keeping you warm. What are the choices? And what is a good system for you on your outdoor adventure?\r\nInsulating Fills and Fabrics Insulation can come in two forms, by way of fill or fabric. Insulating fills are loose down plumes or synthetic filaments that are contained by lightweight fabric. Insulating fill works by trapping body heat within the spaces between the clusters or filaments. Insulating fabrics (fleece, softshell and wool) use their tightness of weave to trap heat and prevent air from permeating.\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 insulation choices can range from lightweight down shirts all the way up to the most insulating parkas for the coldest conditions. Down is best in cold climates and where less weight is optimal, as the warmth-to-weight ratio is the highest.