GRUNDIES PANT BASE LAYER A fantastic upgrade to our ever-popular base layer and mid-layer: Fiske Skins and Arctic Skins. The new GrUndies Base Layer is made from a super comfy and high performing Merino Wool, Polyester Hollow Core, spandex blend that guarantees to keep you toasty under any Grund0ns Rain Gear. This all new style combines the light weight of the Fiske Skin with the warmth retention and comfort of the Arctic Skins.