Our Zip Sleeper is made from a light-weight, soft bamboo fabric that is perfect for summer. Each sleeper includes a convenient two-way zipper to make diaper changes easier than ever. All sizes have fold-over feet to keep toes cozy during nap time. Sizes up to and including 12-18 also have fold-over mittens. Please see our size chart in the listing. These are designed to be snug-fitting. 95% viscose from bamboo, 5% spandex.