MTL (mouth-to-lung) vaping means drawing vapour into your mouth first and then inhaling it, much like a cigarette, using a tight airflow and a higher-resistance coil of roughly 0.8 to 1.2 ohms. RDL (restricted direct lung) means inhaling straight into the lungs through a looser, but still slightly restricted, airflow, usually with a lower-resistance coil of around 0.4 to 0.6 ohms. Choosing the right style, and the right pod resistance...