This study is a comment on “Numerical investigation on cooling performance of hot stamping tool with various channel designs” (Hu et al., Applied Thermal Engineering 96 (2016) 338-351, cited as Ref. 1 in this study). Conformal cooling (CC) channels can significantly improve product quality and production efficiency, such as the reduction of differential shrinkage, warpage, and other surface defects and the shortening of the injection molding cycles. The Reynolds number is an important parameter to determine the cooling performance in CC molds. There is an optimal Reynolds number value below which the cooling is not sufficient and above which the cooling performance is not further improved but the pressure drop rises significantly. Ref. 1 proposed the optimal Reynolds number was 100,000 which is not convincing as such large a Reynolds number value will cause an unacceptable significant pressure drop in the channel. To verify and clarify this, numerical simulations were conducted using the same methods, conditions, and parameters as Ref. 1. The optimal Reynolds number was found as 20,000 rather than 100,000, which was approximately consistent with the results in other reliable references 2,3 rather than the result in Ref. 1.