Experiments have been performed to investigate the cooling performance of triangular folded fin heat sinks made of 6000 series aluminum in a duct flow. The dimension of the triangular folded fin heat sink is 70 mm in width and 92 min in length with an 8-mm-thick base plate. The fin height is varied from 19 to 36 mm and the fin pitch from 5.0 to 9.0 mm. The duct air velocity is in the range of 1.0 to 5.0 m/s and the corresponding Reynolds number based on the hydraulic diameter is varied from 212 to 1974. The experimental results show that the cooling performance of triangular folded fin heat sink is influenced by the fin pitch, the Reynolds number, and the fin height. It increases substantially as the fin pitch decreases and the Reynolds number and the fin height increase. By compiling the experimental data, the heat transfer and the friction factor correlations with +/- 6.5% and +/- 20% accuracy, respectively, are provided for effective design of triangular folded fin heat sinks.