An experimental investigation was conducted to study the performance of film cooling injection from a cylindrical hole and a “W-shaped” hole. A Pressure Sensitive Paint (PSP) technique was used to map the spatial distribution of film cooling effectiveness on the surface of the test plate based on a mass-transfer analogy. The effects of mass flux ratio and density ratio on film cooling effectiveness are investigated by performing PSP experiments at various mass flux ratio using two coolant gases. In order to investigate the kinematic relationship between film cooling effectiveness and mass flux ratio, a high resolution PIV system was used to conduct flow field measurements. Interactions between the mainstream flow and injection flow are also investigated to elucidate the kinematic mechanisms of film cooling.