Polymer films darken upon irradiation with energetic ion beams. At high doses (1016–1017cm−2) of 2‐MeV Ar+ions, the resistivity of these insulating films decreases dramatically to 3.5×10−3&OHgr; cm. Furthermore, over a wide range of doses (1014–1015cm−2) these films exhibit a temperature‐dependent resistivity characteristic of carrier transport via hopping between isolated conducting islands. Rutherford backscattering measurements indicate that while a substantial amount of the carbon is retained in the film, other constituent elements are lost. Raman spectra show that the films are highly disordered at large ion doses.