It is very important to understand that the values of these three components of the capacitor model are frequency depended. With this as background, we may now turn to some of the common capacitor specifications encountered in data sheets. This refers to capacitors where the dielectric is formed by an electrolytic process. Wet electrolytic capacitors have an actual moist electrolyte, while dry or solid electrolytic capacitors don't. However, they are polar devices and in general cannot withstand reverse voltages, and have high ESRs.
Most electrolytic capacitors are aluminum electrolytics.
Tantalum electrolytic capacitors are more expensive but have desirable properties such as higher volumetric efficiency and lower ESR than aluminum electrolytics. This is the nominal value of the capacitor. Since the actual value is a function of temperature, frequency, and to a lesser extent the voltage at which the capacitance are measured, the measurement conditions must be specified. The ESR is used to model the total losses in a capacitor. It is popular because it is a single number, supposedly easing comparisons between capacitors.