There are about twenty common solid dielectrics and about a dozen fluids commonly used in pulsed capacitors. In high repetition rate discharge circuits where very high average and RMS currents can be attained, these materials are reduced to just a few. Dielectrics suitable for this duty must have several specific characteristics. One, small temperature coefficient, that is, the dielectric constant should remain constant over a large range of temperatures. Low dielectric loss is essential for high repetition rate capacitors because, at large RMS currents, substantial heat can be generated in even the smallest of dissipative elements. This is all important in spirally wound capacitors because the only path of heat removal is by conduction out through the foil edges. Pulse capacitor dielectrics should also exhibit constant characteristics with frequency. Since pulse capacitors are exposed to a wide range of frequencies, fluctuations in dielectric constant and loss are not a desired characteristic. Frequency dependence of capacitance and loss further reduce the number of suitable dielectrics for high repetition rate applications. Last, many dielectrics exhibit an electric field dependence, usually given in data sheets as the "voltage coefficient". As with temperature, this parameter is commonly stated as a negative percentage. The magnitude of this effect depends on material properties and mechanical forces. Dielectric constant variations with electric field are determined empirically for the most part. Some spirally wound fluid impregnated capacitors were found to exhibit electrical characteristic changes due to movement of the capacitor plates.