Japanese brand Zerofit is introducing what it calls "the world's warmest base layer" and this is all thanks to patented Heatrub technology that allows for plenty of mobility. In fact, the brand's product claims to be five times warmer than a standard base layer and it's backed by ratings from the Boken Institute in Osaka. While a regular sweater would be rated around 0.3 and a standard base layer might come in between 0.1 and 0.14, Zerofit's innovations are rated 0.78.
Unlike base layers that rely on compression, Zerofit base layers boast five separate fabrics and a patented knitting process that traps body heat between the material and skin. As its name suggests, the Heatrub technology has soft fibers that create friction against the skin to provide warmth and comfort for cold winter activities.