The temperature coefficient is negative and nearly linear. Construction with this dielectric is typically extended foil in either the film and foil types or metallized constructions. The foil may be either aluminum or tin. The metallized types offer vapor deposited metal electrodes and gives significant size savings. Self-healing removes a fault or short circuit by vaporizing the electrode in the region of the short and restores the capacitor to useful life, thereby greatly extending the lifetime of the capacitor.
Typical encasements are wrap and fill, preformed box, epoxy or durez dipped and metal enclosed.
Since polypropylene is not very sensitive to moisture absorption, versatile encasement is possible. This rules out some types of encasement. Physically small parts may experience problems in attachment to the circuit boards unless attention is given to thermal aspects.