Thermal diffusivity results obtained with the collinear mirage technique, are reported for different concentrations surfacted ferrofluid and for a set of acid ferrofluids with variable pH values. The collinear mirage technique was used because the materials are semitransparent and have low thermal diffusivities. The results show that, as the ferrofluid magnetic particles concentration increases, the thermal diffusivity also increases. Their behaviour differs from that reported for ferronematics [1]. The different geometry of thermal waves propagating through the material can account for the difference.