We report the effect of adding up to 23% tin to the indium film of a thin‐film/tantalum‐oxide/bulktantalum transmission line. Addition of tin reduces the velocity and increases the delay for fixed length by 1.4% for each percent of tin. Agreement with the predictions of Pippard's nonlocal theory when meanfree path is reduced is excellent. Pulse attenuation and shape degradation are not increased by addition of tin. Attenuation as low as 10 dB per microsecond of delay was observed at 1.25 K. The added tin reduces by 50% the sensitivity of velocity to temperature nearTc, and improves the reproducibility of velocity from line to line. Critical temperature is increased to 6 K for 23% tin, in good agreement with previous measurements.