Polytetrafluorethylene (PTFE, Teflon) is almost impossible to process by chemicals since it is practically inert against attacks by almost all chemicals, with the only exception of alkaline metal solutions which have an etching effect on PTFE surfaces under formation of alkaline fluorides. A plasma treatment in the low-pressure plasma with hydrogen as a process gas presents an excellent alternative. Here, the hydrogen radicals react with the fluorine in the PTFE to form hydrogen fluoride, leaving unsaturated carbon bonds which are good bonding spots for the attachment of the molecules of liquids. Plasma etching improves the adhesiveness of PTFE, but only with a carefully controlled process. During the etching process, the colour of the PFTE surface changes from almost white to brownish. Plasma etching of PTFE can avoid the problematic handling of the highly aggressive alkaline solutions. PTFE etching in the low-pressure plasma is also referred to as PTFE activation.