22" - 24" woks are traditionally round bottomed. This design ensures that high temperatures are easily achieved while limiting the amount of oil food is exposed to. Woks are primarily intended for stir frying but can also be used as a lower layer for steaming or for deep frying. 22" - 24" woks with deeper shapes and lower capacities are ideal for either cooking method, while san bai woks are used to broil dishes, which makes their snug-fitting lids a core feature. San bai broilers require less control, so they are usually designed with two short side handles rather than the single wooden handle needed to toss food in traditional woks. Cast iron is the traditional metal used for woks, since it withstands extreme heat and conducts well. Aluminum is the preferred metal for broilers because it distributes heat evenly. Curved rim woks produce the best results on gas stoves but flat bottomed designs have been developed to increase heat exposure so that they can be used on electric stovetops.