A comparison between the inner regions of self‐preserving turbulent boundary layers over an impervious wall and a porous surface with a uniform moderate suction rate indicates that, in each case, the relevant velocity and length scales are those of the ‘‘active’’ motion. There is close agreement between the two flows for velocity and temperature variances and longitudinal heat fluxes when the measurements are conditioned on only the negative part of the Reynolds shear stress and are normalized by the scales of the active motion