Currently, carbon steel is the most widely used material, being relatively inexpensive compared with other materials, relatively light in weight, providing quick heat conduction as it has a low heat capacity, and having reasonable durability. Their light weight makes them easier to lift and quicker to heat. Carbon steel woks, however, tend to be more difficult to season than those made of cast-iron ('seasoning', or carbonizing the cooking surface of a wok, is required to prevent foods from sticking and to remove metallic tastes and odors). Carbon steel woks vary widely in price, style, and quality, which is based on ply and forming technique. The lowest quality steel woks tend to be stamped by machine from a single 'ply' or piece of stamped steel. Less expensive woks have a higher tendency to deform and misshape. Cooking with lower quality woks is also more difficult and precarious since they often have a "hot spot". Higher quality, mass-produced woks are made of heavy gauge (14-gauge or thicker) steel, and are either machine-hammered or made of spun steel. The best quality woks are almost always hand-made, being pounded into shape by hand ("hand hammered") from two or more sheets of carbon steel which are shaped into final form by a ring-forming or hand-forging process.