Wear as a base layer in cold and cool weather, and as nightwear in a sleeping bag - Merino wool will keep you comfortable. The material resists odours and is comfortable to wear even when damp. In Smartwool's "core spun" technology, merino wool is spun on top of a nylon core - this structure is more durable than 100% merino wool. It also means that even though the material contains synthetic fiber, your skin is only in touch with merino wool. - The material is 87% merino wool and 13% durable nylon - Material thickness 150g / m² (relatively light) - The wide waistband is lined with merino wool - Machine washable