The bain-marie comes in a wide variety of shapes, sizes, and types. Traditionally it is a wide, cylindrical, usually metal container made of three or four basic parts: a handle, an outer (or lower) container that holds the working fluid, an inner (or upper), smaller container that fits inside the outer one and which holds the material to be heated or cooked, and sometimes a base underneath. Under the outer container of the bain-marie (or built into its base) is a heat source. Using different working fluids (oils, salt solutions, etc.) in the lower container will result in different maximum temperatures.