We integrated world famous Merino wool and our MTF (moisture transfer fibers) into a single base layer and voila, We got this extremely soft, stretchy and functional layer called the Merino Wool Stretch. Hypo-allergenic and stretchy this wool base layer moves with your body while also helping to keep you comfortable and dry. Hot Chillys added moisture transfer fiber panels in the key sweat places you need it the most to provide you with an easy layer that you won't want to live without.