There are alpinists who switch in and out of midlayers between treks and resting spots, and there are alpinists who just wear the Mountain Equipment Men's Switch Jacket. This hybrid midlayer uses moisture-managing fleece at the sleeves and air permeable Polartec Alpha insulation at the body. Compared to standard breathable garments, Polartec Alpha starts breathing the moment you put it on to keep you prime when the ascent gets sweaty.
