Additionally, audio components may report a "Q factor", incorporating ESR among other things, at 1000 Hz.
In many cases this can be done to a sufficient extent that parasitic[1] capacitance and inductance of a resistor, for example, are so small as not to affect circuit operation.
An inductor consists of a conducting insulated wire coil usually wound around a ferromagnetic core.
The DC wire resistance is an important parameter in transformer and general inductor design because it contributes to the impedance of the component, and current flowing through that resistance is dissipated as waste heat, and energy is lost from the circuit.
It can be modeled as a resistor in series with the inductor, often leading to the DC resistance being referred to as the ESR.
[3] ESR can increase enough to cause circuit malfunction and even component damage, although measured capacitance may remain within tolerance.
While this happens with normal aging, high temperatures and large ripple current exacerbate the problem.
Electrolytic capacitors rated for high-temperature operation and of higher quality than basic consumer-grade parts are less susceptible to become prematurely unusable due to ESR increase.
Polymer capacitors usually have lower ESR than wet-electrolytic of same value, and stable under varying temperature.
From about 2007 it became common for better-quality computer motherboards to use only polymer capacitors where wet electrolytics had been used previously.