Ullfrotté Original 400

Positioned firmly between an expedition-weight base layer and a dedicated midlayer, this Swedish-made knit is engineered for punishing cold and low-to-moderate activity. Developed in Östersund alongside the Swedish military, the 400-weight Ullfrotté fabric serves outdoor professionals, winter hunters, and cold-weather campers who spend long, static hours in freezing temperatures. It offers far more loft and raw thermal retention than conventional 200-weight merino baselayers, bridging the gap before needing heavy insulated outerwear.

The hallmark of the garment is its circular knit construction, which eliminates lengthwise torso seams to prevent chafing under heavy pack straps or harness webbing. Inside, dense terry loops of merino wool trap generous volumes of dead air against the skin, creating an exceptional warmth-to-weight profile. By blending fine wool with synthetic polyamide fibers, the construction addresses wool's traditional durability issues, significantly boosting tear resistance and dimensional stability under hard friction.

That thermal efficiency comes with distinct functional limitations. The knit is open and porous, meaning any stiff breeze cuts straight through it unless paired with a dedicated windshell or hard shell. It is also excessively warm and bulky for fast-moving aerobic pursuits like ski mountaineering, where sweat can outpace drying times. Against standard polyester fleece or pure merino midlayers, however, Ullfrotté holds warmth significantly better when damp, making it an unrivaled thermal workhorse for sub-zero fieldwork.