Coils are the heating element that evaporates the e-juice. Without coils, heat does not generate. Coils come from various types of materials, and each material can affect the vaping experience. Some of the most common types of coil materials are stainless steel, ceramic, titanium, kanthal, nickel, and nichrome.
The coil creates heat by resisting the vape's electrical current once you press the button to turn on. As the electric current travels upwards, it eventually gets to the coil, where the coil's rings resist the current flow. Since the electrical current can not travel freely, it lets off energy in the form of heat, making the coils red hot.