Carbon-carbon composite materials are used for plasma-facing applications in fusion energy devices. Next generation fusion reactors will produce high energy neutrons which damage the plasma facing materials and degrade their properties. Here the results of two irradiation experiments, HTFC-1 and -2, each containing specimens of carbon-carbon composites are described. Data are reported for the dimensional changes of the materials as a function of fluence in the range 0.5-5 dpa for an irradiation temperature of 600°C. The observed dimensional changes are analyzed in terms of the composite's architecture, fiber precursor, and graphitization temperature. Dimensional change “turnaround” behavior is observed for several of the materials. Strength is shown to increase with increasing neutron fluence for most of the carbon-carbon composites. High temperature thermal conductivity is reported for two 3D carbon-carbon composites, before and after irradiation. Irradiation reduces thermal conductivity by 60%. However, after thermal annealing at 1600°C the reduction in thermal conductivity is as little as 20%.