A mid-layer or thermal layer is the insulating layer between the first and third layers when implementing the layering principle. The thermal layer for men keeps you warm and dry at the same time. Depending on use, DYNAFIT selects different materials. Fleece jackets with Polartec® ThermalPro® are made for cold days on the mountain. Polartec® Powerstretch® is a very thin, stretch fabric ideal for classic ski touring and alpine running. Polartec® Alpha® is the time-tested fabric for intense sports such as Ski Running, Speed Touring and Speed Mountaineering.