Since natural convection heat sink efficiency degrades with decreasing sink-to-ambient temperature differential, a correction factor must be applied to the published data if an application requires a sink-to-ambient temperature rise of less than 75°C. The corrected thermal resistance is obtained by multiplying published °C/W/3-in data by the appropriate factor from the following table:

For any extrusion profile in natural convection, the thermal resistance (°C/W) is more than 25% higher at DTsa = 30°C than at DTsa = 75°C.