Designed to be safe sleep, diaper change friendly & temperature-regulating. Exterior: 97% Bamboo Rayon, 3% Spandex Filling: 100% Polyester Highly breathable J-shaped double zipper This sleep sack has treated my babies well. They are in well loved condition with some pilling, fading and discoloration (as noted in the photos above) but still lovely and functional. Seam has been repaired as pictured above