A reverse blade fan has its blades curved the opposite way to a standard fan, so it moves air in the opposite direction while keeping the same face pointing at you. That solves a specific problem in modern glass-side builds, where a normally mounted intake fan shows its bare frame and cabling side to the window.

This matters most in cases with side mounted or bottom mounted intakes visible through the glass. With a standard fan you choose between correct airflow and a tidy appearance. With a reverse blade fan you get both.

Cooling performance is unchanged in principle, since the blade profile is mirrored rather than compromised. Choose it for placement and appearance, and read the airflow and static pressure figures exactly as you would for any other fan.