Akasa's Revo heatsink is known as a Loop Thermosyphon Cooler; it functions along the same lines as a heatpipe but relies on gravity instead of capillary forces to return its 'working fluid' back to the hot side. The working fluid is what conducts heat absorbed by the heatsink, from the processor to the heat exchanger, where forced air passing over cooling fins removes it to the surrounding environment. Unlike heatpipes which typically use water under a slight vacuum for working fluid, the Revo heatsink is slightly pressurized with a fluorocarbon called R134a.