Very warm,  box wall constructed Prime Soft® insulated with a light, durable mini rip Stop DWR finish fabric. The Yak stands on its own to deliver cozy warmth in cold, dry conditions. The new Thin Prime soft® provides exceptional warmth for its weight, is durably resilient, and packs easily. As it is designed to function as standalone, not as midlayer. The box wall construction is to deliver maximum loft. The outer is soft, durable 100% Nylon, a lightweight material that withstands abrasion, packs compactly and has a DWR finish to repel moisture. A wind flap is tucked behind the front zipper to suppress drafts.