Bottombumpers outer layer is constructed of waterproof PUL knit outer. Our PUL is soft and stretchy which makes it great for sensitive skin. Bottombumpers keep the wing snaps concealed inside the PUL and lining so they dont touch baby's skin. This also helps prevent red marks. Bottombumpers use high quality industrial strength polyresin snaps. Our snaps are also backed with an hidden extra layer of fabric for extra strength and durability