Check the listing for details. Zerofit Ultimate Heatrub Baselayer Top - Grey. Condition: New with tags. Listed at 85.51 USD. Our most popular baselayer across the entire collection, the award-winning Zerofit Heatrub Ultimate is a best-in-class, game-changing baselayer that has been independently tested and proven to be five times warmer than leading competitors, and twice as warm as a sweater. Technologically enhanced 'Heat Threads inside the garment are activated through even the slightest of movements, gently brushing against the skin to generate positive warmth instantly and the construction of the Zerofit Heatrub Ultimate means the heat is retained. The Heatrub Ultimate baselayer has been engineered to stretch to the demands of many outdoor SPORTS and activities, and although the size chart shows optimum chest sizes, the Ultimate is engineered using an incredible four-way stretch fabric for incredible flexib.