Irradiation of thin commercial sheets of poly (tetrafluoroethylene) (PTFE) or a fluorinated ethylene-propylene copolymer (FEP) yield essentially the same results with mass spectroscopy or x-ray photoelectron spectroscopy (XPS). For both gas phase and surface (ca. 30 angstrom) products of irradiation, the same product distributions and exposure dependencies are observed. In addition, XPS of chemically etched (with sodium naphthalenide) PTFE and FEP shows the same extent of surface defluorination. In contrast to the more surface-sensitive XPS, Rutherford backscattering spectroscopy of etched PTFE shows that the defluorination extends to depths of ca. 3000 angstrom, while with etched FEP defluorination extends to only a few hundred Angstroms. Scanning electron microscopy shows the FEP surface to be smooth and featureless both before and after chemical etching, while etched PTFE is characterized by a crazed surface with a high density of unidirectional cracks oriented perpendicular to long macroscopic scratches existing in the virgin surface. Adhesion of Cu to this etched PTFE has previously been shown to be sufficiently strong that failure is a result of near-cohesive failure in the PTFE and not adhesive failure. Conversely, weak adhesion of Cu to etched FEP or to other smooth forms of fluorinated polymers, including polished PTFE, is observed. This correlation of strong adhesion with surface roughness and not with surface chemical changes is consistent with previous suggestions that a major component of adhesion to fluorinated polymers is mechanical interlocking. The differences between FEP and PTFE are discussed in terms of a model involving surface stresses expected from their different methods of manufacture : extrusion from the melt in the case of FEP and skiving from pressed cylinders in the case of PTFE.