Mackey Flexi Full Cheek Mullen Mouth Snaffle Bits are created with a polyurethane material, which is both lightweight and flexible. The material’s softness makes it kind on the horse’s mouth, making this bit ideal for young horses, horses that have just been backed, and those that do not respond to a standard steel bit. With an extensive selection of styles, each have their own unique properties that are slightly lessened by the warmth and flexibility of the polyurethane.