One of the most important characteristics of a zipper is the material of the zipper teeth—whether Molded Plastic, Nylon Coil, or Metal, each material of zipper teeth has its own advantages and ideal uses. Molded Plastic materials is flexible and lightweight. Nylon Coil is very flexible and durable because of the “coiled” tooth design, allowing it to withstand more horizontal strain. Metal is very durable and eye-catching with many options (aluminum, antique brass, antique nickel, black oxide, brass, gunmetal, and nickel). Best for straight seams as they are not as flexible, and less suited to horizontal stress.