The effects of Nd ₂ O ₃ doping on the thermal and mechanical properties of vacuum melted, low silica, calcium aluminosilicate glasses are presented. For the doped glasses, the vitrification limit was found to correspond to a maximum load of 5 wt % Nd ₂ O ₃ . The influence of the rare earth doping on the thermal diffusivity, thermal conductivity, and Vickers hardness was such that all these physical parameters decreased by roughly the same amount, namely 8%, between the undoped and the 5 wt % doped sample. The dependence of these parameters, as a function of the Nd ₂ O ₃ doping, strongly supports the idea that the Nd ³⁺ act as network modifiers. © 1999 American Institute of Physics.