E-cigs have two types of refills: cartridges and cartomizers. The key difference is: Cartomizers have “built-in” atomizers; Cartridges don’t. Cartomizers cost a little more but last longer (the equivalent of a little more that a pack of cigarettes) and they are self-contained - just use one and throw it away, each cartomizer has a new built-in atomizer.
Cartridges cost less, but last the equivalent of 5 or 6 cigarettes … and cartridges won’t work without atomizers, which are sold separately. (Atomizers heat the liquid causing vaporized mist.) Both contain liquids that vaporize; Both come in varying levels of nicotine – high, medium, low or none; And both come in a variety of flavors – tobacco, menthol, apple, vanilla, etc... Some prefer the taste of one over the other – but that’s personal preference. … And if you’re a “do it your self’er,” it’s easier to inject refill-liquids into a cartridge.