The problem. If you alternate effort and stops you need a layer that keeps you warm at rest and doesn't make you sweat when you set off again: climbs and descents, chairlifts, outdoor shifts.
How it solves it. The DHtech 400 Tunnel sweatshirt is knitted as a tube: an air gap between the two faces of the fabric holds the warmth when you stop and lets vapour out when you move. Full zip and hood.
The proof. Like all DHtech fabrics it is made of polypropylene, the fibre that absorbed the least water in DryHeat Lab tests: a 0.13% weight gain after absorbing liquid, versus 0.72% for polyester.
How to wear it. Over a DryHeat base layer: DH Extreme Power if you push hard, DH Drywool if it's very cold. Under your jacket on windy days.