The hydrophobic properties of carbon fibers improved by a CF4 plasma treatment were used to fabricate gas diffusion layers (GDLs) for use in proton exchange membrane fuel cells. The water contact angle of the CF4 plasma treated GDL was measured as 132.8 +/- 0.2 degrees at 45 degrees C and very few surface gas diffusion pores were either sealed or blocked by the excessive hydrophobic material residuals. Polarization measurements verified that the CF4 plasma treated modules can indeed enhance fuel cell performance, compared to the membrane electrode assemblies (MEAs) with a non-wet-proofed GDL, 10 wt% PTFE dip-coated GDL, and commercially available GDL (10 wt% PTFE). (c) 2006 Elsevier B.V. All rights reserved.