In simple terms, a Capacitor is a device whose function is to store the heat energy inside it and deliver the energy when required. An Insulator is the one whose function is to stop the heat transfer from one device to another, i.e., it doesn’t allow the heat to get transferred. Capacitors are widely used in the digital board circuits and semiconductor industry.
If you ever checked the Capacitor, it will have two wires or points coming out the one terminal is the positive one and the other one is the negative one.
Insulators vary the application from various areas. Insulators are a common material for the adventure sports like mountaineering, where it is used to keep heated tents.
The Insulators are much cheaper than the Capacitor as they are made up of simple plastic and rubber, which is easily available.