The tribological properties of most high functioning tribological materials, including diamond, graphite, molybdenum disulfide, and polytetrafluoroethylene, depend strongly on environmental moisture. A particularly wear-resistant alumina–polytetrafluoroethylene (PTFE), for example, loses its capacity for ultralow wear in dry environments because a moisture-dependent tribochemical degradation product is necessary to anchor and stabilize its protective transfer films. A recent study Onodera et al., J. Phys. Chem. C, 2017, 121, 14589–14596 on a PEEK–PTFE composite suggested that the poly­(etheretherketone) (PEEK) filler particles anchor PTFE transfer films to metallic surfaces via physical interactions that are, theoretically, insensitive to environmental moisture. This study tested the hypothesis that the physical nature of transfer film adhesion by PEEK–PTFE increases its wear tolerance to changes in environmental moisture. The optimal 20 wt % PEEK–PTFE composite exhibited the same ultralow-wear rates (8 × 10–8 ± 1 × 10–8 mm3/Nm) and low friction coefficients (0.18 ± 0.02) in dry nitrogen (0.05% RH) and humid air (30% RH). The results demonstrate that this unusually wear-resistant solid lubricant material is also unusually insensitive to environmental moisture. Compared to the well-studied alumina–PTFE system, whose ultralow-wear rates correlate strongly to the prominence of carboxylate peaks in infrared (IR) spectra, carboxylate peaks were either greatly attenuated or absent in the IR spectra of PEEK–PTFE following ultralow-wear sliding in both humid and dry environments. The results are consistent with the prediction from the Onodera group that the ultralow-wear rates of PEEK–PTFE can be retained in dry environments because the strong physical interactions between the PEEK filler and the counterface reduce or eliminate its dependence on water-dependent tribochemistry for transfer film adhesion.