Plastic-film capacitors

Various different plastics make good dielectrics for the manufacture of capacitors. Polyester, polyethylene, and polystyrene are commonly used. The substance called mylar that you might have seen used to tint windows makes a good dielectric for capacitors. The method of manufacture is similar to that for paper capacitors when the plastic is flexible. Stacking methods can be used if the plastic is more rigid. The geometries can vary, and these capacitors are therefore found in several different shapes.
Capacitance values for plastic-film units range from about 50 pF to several tens of microfarads. Most often they are in the range of 0.001 μF to 10 μF. Plastic capacitors are employed at audio and radio frequencies, and at low to moderate voltages. The efficiency is good, although not as high as that for mica-dielectric or air-dielectric units.