The pajamas are made of 100% ribbed cotton. The fabric has a comfortable stretch and includes snaps at the back and legs. Machine washable. Please make sure to try on the pajamas before washing to make sure they fit as you can"t return pajamas once they are washed. Sizes run as follows: 6 Month, 12 Month, and 18 Month. Sizing runs true to size (height/weight): 6-12 Months (27-29" / 17-21 lbs), 12-18 Months (29-31" / 22-25 lbs), 18-24 Months ( 31-33" / 27-30lbs)., not flame resistant, must wear snug fitted.