Abstract: A data storage medium is provided which is suitable for production or replication by moulding, casting, embossing or a similar process against a tool. The data storage medium has a surface or a surface region which is strongly absorbent of at least a predetermined band of wavelengths of electromagnetic radiation. The surface or surface region includes a layer of a heat sensitive material which has a textured surface pattern the pitch of which is smaller than the shortest wavelength of the predetermined band of wavelengths, and the depth (peak-to-trough) of which is at least 100 nm. The surface pattern is free from undercutting, and can comprise an array of protuberances or one or more sets of grooves (which may be intersecting). The textured surface pattern is further coated with a thin film of a high-opacity material, e.g. gold, the thickness of the overcoating preferably being such as to give no more than 10% transmission of incident radiation.