Some of the shoes in Keen's line for this coming fall/winter season will feature its new heat-trapping technology, Keen Warm Plus. The innovation stores and traps air that has been warmed up by the body. Usually this warm airs leaks out through the soles of shoes, but Keen Warm Plus is made up of three layers of heat-trapping material to keep warmth in and cold out. It adds on to Keen Warm, an insulating antimicrobial material based on bamboo charcoal. The Revel men's boot is one of the styles that will use the new technology.