All‐optical fabrication of elastic volume diffraction gratings in polydimethylsiloxane (PDMS) is presented. Novel material based on the commercially available PDMS with incorporated benzophenone (BPh) photoactive molecules is developed. The gratings are formed by a holographic technique and UV irradiation through an amplitude mask. New material permits to obtain efficient volume gratings with periods ranging from hundreds nanometers to dozens of micrometers in elastic films of different thicknesses. Besides symmetric transmission 1D gratings, slanted and 2D gratings have been fabricated as well. Photoattachment of BPh molecules and their real‐time diffusion within elastic PDMS matrix in accordance with the spatially modulated light is considered as a mechanism of the gratings formation. The refractive index modulation amplitude of about 7.0 × 10−4 is achieved. It is shown that mechanical strain of the elastic volume gratings allows fully reproducible alteration of the gratings parameters. In order to tune the diffracted wavelength over the whole visible spectral range (from 410 up to 700 nm), a strain of about 75% is required. New volume diffraction PDMS gratings represent very successful combination of cheap and widely known materials with one‐step optical fabrication techniques providing high‐performance tunable diffraction elements that can be applied in photonics, sensing, and spectroscopy.