A lightweight plastic lens material that is easily tinted to just about any color. Standard Plastic CR-39 Lenses are much lighter and less breakable than glass lenses. Traditional plastic lenses are made from a hard resin that is cast or moulded in the wet state into lens blanks. These plastic blanks can be ground into specific shapes to fit any lens frame. Plastic lenses are great for prescription sunglasses due to their tintability factor.