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The women's REI Silk long underwear bottoms are smooth, soft and incredibly comfortable. They'll help keep you warm on a cold day and they work great under additional layers. Lightweight, breathable, pure silk jersey is enhanced with a wicking treatment to help keep you dry and warm. Wide, self-fabric elastic waist, seamless sides and rib-knit cuffs provide a comfortable fit throughout. Fabric is substantial yet thin enough for everyday wear under jeans or casual pants. Machine wash warm on gentle cycle without bleach or fabric softeners, tumble dry low.