•The bremsstrahlung DDCSs are measured at 90° with 5–25 keV electrons for C and Al.•The bremsstrahlung photons are measured down to 1–2 keV.•The measured DDCSs are compared with OB and SA theories.•It is found that the discrepancies between the measured data and the theories exist. Absolute measurements of the bremsstrahlung double differential cross sections (DDCSs) for photons radiated at 90° generated by the collisions of 5–25 keV electrons and down to 1–2 keV photon energy with two thin targets C (Z = 6) and Al (Z = 13) are presented. A parallelized version of the PENELOPE Monte Carlo program has been used to correct the effects of electron multiple scattering and the backscattering from the target substrate on the experimental results. Comparisons between the experiments and the theories reveal some discrepancies between the measured data and the theoretical bremsstrahlung predictions.