MTL vaping, also known as mouth-to-lung vaping, is the style of vaping where you use your vape like you would smoke a cigarette. So you take it back into your mouth, and then inhale the vape into your lungs, before exhaling. This is the most popular style for quitting smoking, and users will usually use the 50/50 liquid. DTL, direct-to-lung, or STL, straight-to-lung vaping is different. In this style you would inhale the vape straight back into your lungs. In general, this produces more cloud and flavour for the user and is popular with lower nicotine users who are chasing flavour.