E- cigarettes consist of a battery, processor, and cartridge. A filter end holds a cartridge containing a nicotine solution. The liquid that contains the nicotine is usually propylene glycol or glycerin with added flavorings. Nicotine concentrations vary and are sometimes inconsistent in lab testing. Cartridges don't ’burn down’ but deliver a puff when inhaled. With every drag, a pressure sensor switches on and an electric heating coil vaporizes the glycol solution, releasing steam through the mouthpiece. Because vapor is released, the term "vaping" was coined.