Film type resistors

Carbon, nichrome, or some mixture of ceramic and metal (cermet) can be applied to a cylindrical form as a film, or thin layer, in order to obtain a desired value of resistance. This type of resistor is called a carbon-film resistor or metal-film resistor. It looks like a carbon-composition type, but the construction technique is different (Fig. 1).

Fig. 1: Construction of a film type resistor.

The cylindrical form is made of an insulating substance, such as porcelain. The film is deposited on this form by various methods, and the value tailored as desired. Metal-film units can be made to have nearly exact values. Film type resistors usually have low to medium-high resistance.
A major advantage of film type resistors is that they, like carbon-composition units, do not have much inductance or capacitance. A disadvantage, in some applications, is that they can’t handle as much power as the more massive carbon-composition units or as wirewound types.