Silk fibroin films in the random‐coil and β‐form conformations were immersed in water at temperatures from 2 to 130°C, and conformational changes were followed by x‐ray diffraction, infrared spectroscopy and differential scanning calorimetry. On treatment with water below 60°C, the random‐coil conformation is converted to the α form and above 70°C to mixtures of the α and β conformations. The β‐form content increases as the immersion temperature is raised. The β form is not affected by immersion in water in the temperature range studied.