A multifunctional hypothesis of filler selection for PTFE suggests ultralow wear (10−7 mm3/Nm) depends on the filler’s ability to both support the normal load by being large in size and to induce favorable tribochemistry by being weak in aggregate strength. This study is the first to test the independent effects of preferential load support and tribochemistry on PTFE wear by studying the wear reducing properties of a porous GaN fiber, a fully dense SiO2 fiber and microsized GaN particles. The results found the only filler that induce ultralow wear is the GaN fiber which was microns in size and friable under shear stresses. This study reinforces the leading hypothesis that a mechanistic synergy is required for ultralow wear PTFE composites. •Gallium nitride fibers reinforced PTFE wear rates are over three orders of magnitude lower than unfilled PTFE.•Low wear behavior derived from nanostructured gallium nitride fibers and tribochemically altered PTFE.•Environmental tribology tests and molecular simulations were used for the mechanistic study.•A synergistic anti-wear mechanism of mechanics and tribochemistry was proposed.