Nappies for a snug, leak-free fit. Fitted Nappies are shaped to fit with elastic in the waist and legs. They close with velcro, snaps or a snappi and require a waterproof cover. Fitted nappies can come as a sized system (small, medium, large) as a pocket, one-sized and with snap-in or lay-in booster systems. A fitted nappy in combination with a well fitting waterproof cover is the most reliable of nappy systems as there are two lines of defence against leaks, the elastic in the legs/waist of the nappy and the elastic in the legs/waist of the cover.