Ilford C‐2 unloaded and C‐2 boron loaded plates, subjected to temperature changes varying from −66°C to +66°C, were bombarded with 10‐Mev neutrons. The recoil protons showed that the temperature change had caused an increase in grain density which varied as much as ⅓ from −66°C to +25°C. Although the C‐2 boron loaded plates showed a greater initial grain density than the unloaded plates, the ⅓ increase was preserved.