Abstract The effect of hertzian contact pressure on the friction coefficient of self-lubricating boric acid (H3BO3) films was investigated by sliding steel and ceramic balls against boric oxide (B2O3) coated steel and ceramic disks under a wide range of contact loads. Self-lubricating H3BO3 films result from a spontaneous chemical reaction between water molecules and B2O3 coatings in humid air. Mean initial hertzian contact pressures in the range 0.31–1.6 GPa were created between balls and B2O3-coated disks by varying the applied load and the radius of the balls. It was demonstrated that an inverse relationship exists between friction coefficient and hertzian contact pressure. Using the hertzian contact model, we estimated that the shear strength of H3BO3 films was approximately 22.9 MPa, which is comparable with 24.8 MPa reported for MoS2.