Description New fabric information in the size chart tab If you're looking for a baselayer to stand up to the coldest winter days Mother Nature throws your way - and we've had customers wear Comet on expeditions in Antarctica and Alaska - then you've come to the right place. Duckworth's proprietary Comet fabric is natural-technical mash-up, combining a fortified Montana-grown Merino Wool outer layer and a recycled polyester inner layer. Why the combo? Polyester is hydrophobic, meaning it will wick sweat and moisture right off your skin and into the hydrophilic wool layer; wool chemically begins to get even warmer when introduced to water and water vapor, thus explaining why the Comet Crew will have you feeling dry and toasty even in the nastiest conditions. By the way, this loose-fitting top is soft to the touch, meaning it works perfectly as a single layer for casual food and drinks in between runs at the ski lodge. Durable, anti-odor, moisture-wicking, quick-drying, and versatile: your one-stop-shop baselayer. Fabric Why Duckworth Comet Fabric?   Composition: 94% Montana Merino Wool and 6% nylon outer layer, 100% recycled polyester inner layer Weight: 315 gsm Sizing & Wool Care NEW FABRIC INFORMATION: You spoke and we listened - following ample customer feedback in combination with Research and Development at the ranch, we've slightly adjusted the outer-layer material to include 6% nylon for the purpose of adding extra strength to the wool yarn. The fabric also features a 315 GSM construction vs 275 GSM in year's past, for optimal warmth and weight in the colds of the American backcountry. Cold gentle machine wash with like colors. Do not bleach. Dry flat or line dry only; do not tumble dry.