100% Nylon. Our kid glasses retainer is designed to keep a tight grip on kid's glasses or sunglasses, preventing the loss of the glasses and breaking during movement or sports, allowing glasses of kid to be comfortably hung on their chest, or rest on top of the head. Using environmental friendly, durable and premium Elastic rope nylon material, They are very well made and strong but soft and flexible at the same time. Elastic design allows you to stretch the kid glasses strap up to 20 inches, which measures approx 10 inches originally. Metal loops at both ends of the straps can be slipped on and off easily, and help to fasten the strap with glasses firmly. Cute cartoon-shaped plastic buckle is decorative and also adjustable to guarantee secure fixation.(Please note: all kinds of cartoon adjustment buckles are randomly matched)