Aluminum was thermally deposited onto fluoropolymer substrates. The effects of interfacial reaction of aluminum with several fluoropolymeric substrates were investigated. These included PFA (poly[tetrafluoroethylene-co-perfluoro(alkoxy vinyl ether)]), FEP (poly(tetrafluoroethylene-co-hexafluoropropylene), and hydroxylated FEP (m-FEP). The hydroxyl modification was prepared by a previously developed radio frequency glow discharge (RFGD) method. X-ray photoelectron spectroscopy (XPS) studies of thin (similar to 30 Angstrom) Al deposited samples showed the formation of new fluorine-containing species, due to fluorine diffusion into the Al overlayers. Auger and XPS depth profiles bf samples with thick (similar to 200 Angstrom) Al overlayers also suggested the diffusion of fluorine and the formation of Al fluorides at the interface. The RFGD modification process prior to the Al deposition was performed to investigate potential adhesion of Al to the substrates. This is envisioned as a reaction between Al and RFGD introduced oxygen. The resulting Al/oxide interface limits the diffusion of fluorine.