The newest innovation in cooling fans from LEPA comes the BOL Quiet Series. BOL stands for Barmetric Oilless, which uses a completely oilless bearing design that lessens the friction in rotation, therefore increasing the fan"s lifespan. Not only does BOL increase the lifespan, but also decreases the noise production and provides an optimal silent operation. The BOL.QUIET PWM stands for Pulse-Width Modulation, which allows your fan to adjust its speed depending on the load of your system (4-Pin fan motherboard header required). This model comes with 4 Blue LEDs that makes for a unique lighting effect like none other.