The surface of ultrahigh molecular weight polyethylene and high density polyethylene was modified using two different fluorination routes: radio-frequency plasma-enhanced fluorination using O2/CF4 mixtures or c-C4F8 and the direct fluorination with 10%F2 + 90%He mixtures. The modification of the surface layers was characterized by FTIR and visible spectroscopy, AFM, XRD, XPS and surface energy measurement. A diffusion-controlled mechanism of the growth of fluorinated layer was confirmed. The dependence of the surface energy values on storage duration was studied. The chemical composition, texture and roughness of the polymer surface strongly depend on the treatment method and conditions. Fluorine concentration varies within the depth from the polymer surface.