Injection moulding of parts having small flow length/thickness ratio is a challenging task for both micro and packaging applications. In the filling phase, high-speed injection can cause a raise of cavity pressure, which prevents the complete replication of the mould geometry. Therefore, in this paper, the effects of mould coatings, e.g. diamond-like carbon, chromium nitride and silicon oxide, were investigated. In particular, the filling of a representative micro-part was studied as a function of mould coating, injected polymer and different process parameters, in order to identify the best processing conditions in terms of cavity pressure and part quality.