95% at 29 microns, just squeaking in the US CAR 36 standard of 95% at 30 microns, interestingly enough.
Champ Labs testing showed 83% @ 25 microns in 2007 for the NAPA and CQ Red variants.
Extrapolation yields 69% at 20 microns to put it at a benchmark most easily compared with other filter published efficiency figures