Intermodulation distortion (IMD) is known to be an impediment to progress in superconductor-based filter technology. The present invention's methodology for reducing IMD can open doors to heretofore unseen practical applications involving high temperature superconductor (HTS) filters. Typical inventive practice includes (a) increasing the thickness d, and/or (b) changing the operation temperature T, of the filter's HTS film. The film's thickness d is increased in such a way as to decrease the IMD power PIMD in accordance with the material-independent proportionate relationship PIMD∝1/d1.5-6. The film's operation temperature T is bettered or optimized in accordance with the material-independent proportionate relationship PIMD∝(λO(T))10(K(2)(T))2/(ΔO(T))6, and further in accordance with three individual material-dependent relationships, namely, between operation temperature T and each of linear penetration depth λO, gap maximum ΔO, and kernel K(2). Some inventive embodiments include oxygen overdoping of the film as an additional/alternative IMD-reductive measure.