The fan stack is an essential part of the cooling tower. It’s located within the propeller fan and prevents reverse running of the fan caused by high input air speed. Because the fan stack is integral to your cooling system, it’s important that it’s made out of durable materials that will keep it functioning properly for longer. What is FRP Fan Stack Material? Fan stacks for cooling towers can be made from laminated polyester or fiber-reinforced plastic, better known as FRP.