Abstract The temperature dependence and strain rate sensitivity of the ultimate tensile was examined in heavily cold-drawn copper, niobium and Cu20%Nb. The results show that the activation parameters for plastic deformation of Cu20%Nb and niobium are similar and are significantly greater than those for plastic deformation of copper. It appears that plastic deformation of Cu20%Nb reflects the deformation behavior of the niobium filaments rather than of the copper matrix.