RDTL vaping is a bit of a hybrid between Mouth to Lung and Direct to Lung. It uses a restricted airflow, which means that you don't get as much vapor as you would with DTL vaping. However, the airflow is still open enough that you can inhale the vapor directly into your lungs. This gives you the best of both worlds, with the flavour intensity of MTL vaping and the cloud production of DTL vaping.