A ductile material can be drawn into wires. A malleable material can be hammered into sheets. Copper and steel are ductile.A strong material is one with a high ultimate tensile strength. This is the maximum stress a material can withstand when being stretched before breaking. Beyond this point, necking may occur.The stress value at the point of fracture is called the breaking strength of the material.Polymers like rubber and polythene can stretch a great deal before breaking. Rubber has a low ultimate tensile strength.A brittle material shows elastic behaviour up to its breaking point and breaks with little or no plastic deformation. Ceramics are brittle.