PET film.

The clear plastic carrier sheet a DTF printer prints ink and adhesive powder onto; the design is not a garment print until that film is heat-pressed and peeled away. Film type sets the peel behavior, hot or cold, and how cleanly the ink releases, so changing film is a press-setting change. It is also one disposable sheet per print, which is where DTF's plastic-waste question comes from and DTG's does not.