Cotton, Made of 100% cotton muslin, our nursing pillow cover are breathable and gentle to touch, offering a soft and comfy surface for baby. Pre-washed for premium softness, these muslin breastfeeding pillow covers are cozy and skin-friendly, delightful for all seasons. Each slipcover fits nursing pillows within 22x17x16.2 inches snugly. Backside large opening is designed for easy putting on and taking off, those soft and breathable nursing pillow cover can be applied within seconds. We adopts hidden zipper closure on backside for baby's maximum safety. Zipper is covered with an extra piece of fabric, it won't be exposed when not in use. All interior seams are professionally finished for durability and longevity of baby nursing pillow cover. Our cotton nursing pillow covers are machine washable, but avoid high temperature, don't bleach.