The report, third in an EPA Fabric Filtration series, gives results of an evaluation of fabric filters made of an expanded polytetrafluoroethylene (PTFE) film supported on a woven Nomex scrim--the Gore Tex/Nomex fabric. Filtration efficiency was very high and other performance parameters (drag and effective cake resistance), acceptable. The one fabric bag tested for endurance failed prematurely near the bag cuff; even so, it gave evidence of acceptable bag life. Because of the small fiber dimensions and spacings of the PTFE film, the dominant mechanism for particle removal appears to be sieving. This mechanism is not usually the dominant filtering mechanism for fabric filters; consequently, the Gore Tex/Nomex fabric exhibits some properties that are different from those of other fabrics evaluated in this series. The most important difference is in the role of the dust cake which, for the system reported here, is not a major factor in determining efficiency. Filtration efficiency is as good or better with little or no dust cake on the filter (such as at the beginning of a filtration cycle) than it is after a cake has had a chance to form (such as at the end of the filtration cycle). Thick dust cakes were simply not seen on this fabric, however. This conclusion applies only to the flyash used in these experiments. Finer dusts may behave differently.