Designed primarily for comfort, the Silk Blend Liner adds warmth to your sleeping bag via the 72% Thermolite Pro yarns with infra red technology, Thermolite EcoMade fibers and 28% silk. The combination creates a soft, luxurious sleep environment. Comfort Stretch Panels along the seams boost sleeping comfort. Shoulder openings and a drawcord footbox add temperature regulation (and match the Free-Flow zippers of Sea to Summit sleeping bags).