Arc'teryx RHO Heavyweight bottom men'sThe Rho Heavyweights our warmest base layer tops are made for cold days and mixed output. On the move, the Polartec Power Stretch Pro stretches for outstanding freedom of movement. During rest phases or when it gets really cold the fleeces soft brushed interior traps heat to keep you warm. The fleeces durable nylon outer has a smooth face for comfort under layers, the tall collar extends warmth, and the deep front zipper aids heat dump and makes on