The permeability of filled PTFE is very dependent upon methods of fabrication. Since there is no chemical bonding between PTFE and the fillers used, the permeability is generally greater .than that of unfilled PTFE, As the filler content increases, particularly above 10% by volume, special care, or special techniques, have to be adopted to ensure minimum permeability.

Specific measurements have not been made, but from porosity tests it is concluded that permeabilities can be made close to that of unfilled PTFE, if the correct method of fabrication is used.

PTFE is one of the most chemically resistant materials known, and fillers can only worsen this position. As with unfilled PTFE, chemical attack on the filled PTFE should not be confused with chemical attack on adjacent parts resulting from permeability of the filled PTFE.