A method of photoprotecting a material against solar UV radiation by treating the material using a composition having a dispersion of photonic particles with a mean size in the range 1 μm to 500 μm, each having a diffracting arrangement of monodisperse nanoparticles or voids, the diffraction spectrum of the arrangement including a first order reflection peak in the wavelength range 250 nm to 400 nm, or by integrating the dispersion of photonic particles into the material.
