A novel microstructuring technique, photoembossing, is used to create relief structures on the surface of fibres to generate new functionalities, such as diffractive optical effects for fashion design. A typical photopolymer compound, which consists of a polymeric binder, a multifunctional monomer and a photoinitiator is coated on the surface of a conventional synthetic core fibre (PET). Photoembossing is performed via a non-contact exposure to an interference pattern to obtain surface-relief gratings with the grating vector along the fibre axis. The monofilament fibres with grating structures perpendicular to the fibre axis were produced with a period of 1 and 8 µm and a typical height of 60–110 nm and 900–1300 nm, respectively. In accordance with the grating equation, it is observed that the micro-structured fibres with a pitch of 1 µm exhibit a strong angular dispersion and this in contrast to fibres with a pitch of 8 µm. Separated diffracted colours are observed predominantly in the first case (red, green and blue) by varying the viewing angle.