300 thread count - 40% NASA-approved Outlast viscose / 60% cotton top cover for peak breathability and temperature-regulation Proprietary Outlast lining fabric for maximum heat management and added comfort Oeko-Tex Standard 100 Certified Technology Designed to work even when used underneath your pillowcase Zippered enclosure transforms your existing pillows into performance "cooling" pillows Mini spacesuits for your pillows. Designed to zip over your current pillows, these covers automatically adapt to temperature changes to maintain cool comfort throughout the night. These state-of-the-art pillow covers incorporate layer upon layer of proprietary Outlast temperature regulating fabric so you are always sleeping on the cool side.