Injection molding of thin-wall parts is a challenge due to the raise of cavity pressure during the filling phase that can prevent the complete replication of mold geometry. The melt flow in thin-wall injection molding is characterized by high shear stress that can modify the no-slip boundary condition at the polymer-mold interface. Mold coatings can be used to reduce cavity pressure by exploiting a combination of thermal isolation of the flow and induction of the wall-slip phenomenon. In this work, the effects of different mold coatings (viz. diamond like carbon DLC, chromium nitride CrN, chromium titanium niobium nitride CrTiNbN) on the efficiency of the filling phase were investigated. The design of the mold allowed the high-speed visualization of the melt polymer flow through the 400 μm thickness of the cavity. The velocity of the polymer melt was evaluated by tracking the coordinates of some silica carbide particles dispersed in the polymer. The results indicated how mold coatings can be used to significantly reduce cavity pressure and thus improve the filling phase in thin-wall injection molding.