Local impermeable wall effectiveness is measured along a concave surface downstream of a row of film cooling jets. Three different injection hole diameters, two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. Except close to injection, where normal momentum is strong, an increase in blowing rate results in improved film cooling performance. This is attributed to an increase in thermal mass (capacity) of coolant, tangential momentum of the jet, and blockage. Far downstream of injection, the normal and tangential momentum weaken, but blockage and large thermal mass at high injection rates still keep effectiveness high. Lateral mixing of the jets caused by the unstable concave mainflow results in film-cooling performance, which correlates well with the same parameter, which is influential in slot injection on a flat surface. Deviation from this twodimensional behavior is found only at very low blowing rates and weak wall curvature.