A (H.sub.2) sensor composition includes a gas permeable matrix material intermixed and encapsulating at least one chemochromic pigment. The chemochromic pigment produces a detectable change in color of the overall sensor composition in the presence of H.sub.2 gas. The matrix material provides high H.sub.2 permeability, which permits fast permeation of H.sub.2 gas. In one embodiment, the chemochromic pigment comprises PdO/TiO.sub.2. The sensor can be embodied as a two layer structure with the gas permeable matrix material intermixed with the chemochromic pigment in one layer and a second layer which provides a support or overcoat layer
