Patagonia Women's Capilene Thermal Weight Bottoms. The warmest, most breathable polyester baselayer with minimal bulk. Excellent cold weather protection. Features: Polartec(R) Power Grid(TM) fabric has a smooth face for easy layering Fabric's open grid pattern next to skin provides superior warmth, breathability and moisture-wicking performance Spandex for stretch and ease of movement Flat waistband has brushed inner elastic for next to skin softness Gusseted crotch for comfort and unimpeded mobility Flatlock seams to minimize chafing 3.8-oz (129-g) Polartec(R) Power Grid(TM) fabric. Solids: 92% recycled polyester/8% spandex; heathers: 91% polyester (30% recycled)/9% spandex; both with Polygiene(R) permanent odor control. Fabric is bluesign(R) approved 138 g (4.9 oz)