Adidas Techfit Climaheat Long Sleeve Stretch Gray XS Material: 77% Polyester, 18% Nylon, 5% Polyurethane The Techfit HEAT series, equipped with climaheat thermal technology, uses hollow-core fibers. These fibers are highly sweat-absorbent and quick-drying, and their hollow structure makes them lightweight, trapping heat to keep athletes warm. Furthermore, the mesh structure prevents heat buildup, and the back heat zone and side sections feature ventilation to release heat appropriately.