Woven Muslin - 100% Peruvian Cotton. Cut loosely like a bubble, this sweet rompers straps have a touch of elastic that cinches gentle ruffles along the neckline. Even better, it opens wide enough to slide up and around the chubbiest baby. MEDIUM-WEIGHT INTERLOCK (Interlock is a knitting technique that sandwiches 2 layers of jersey and results in a smooth surface on both sides, inside and out.)