Concerning a materials ability to convert heat to electrical energy, the electrical power factor S
/ρ as well as the thermal conductivity at elevated temperatures are of special interest. Since Flash experiments measure the thermal diffusivity and standard steady-state heat-flow experiments are inaccurate at elevated temperatures due to radiation errors inherent to this technique, direct and accurate thermal conductivity data on type-I clathrate single crystals at elevated temperatures are scarce in literature. Here we report 3ω thermal conductivity data on single crystalline Ba8Cu5.09Ge40.91 (BCG), La1.23Ba6.99Au5.91Si39.87, and Ce1.06Ba6.91Au5.56Si40.47 in the temperature range between 80 and 330 K, and specific heat data on BCG between 2 and 300 K. The comparison of our room temperature phonon thermal conductivity data (κ
) to results on transition metal (TM) free type-I clathrates in terms of the guest free space (R
free) suggests a stronger dependence of κ
free for the clathrates containing TM elements.