While it wouldn't surprise me if Thermaltake didn't spend many an hour testing fan direction, that's pretty inconsequential. Due to the way the fan's mounted(at least on mine) you can't physically turn the fan around. The only way to reverse the direction of airflow is reversing the polarity of the power to the fan, and I GUARANTEE whoever made the fan did spend many an hour optimizing it for flow in the direction it's going.