Unlike a heatsink, a spreader is meant to redistribute heat, not to remove it. In addition, the IHS protects the fragile CPU. Passive cooling involves no fan noise as convection forces move air over the heatsink. Other techniques Liquid immersion cooling Another growing trend due to the increasing heat density of computers, GPUs, FPGAs, and ASICs is to immerse the entire computer or select components in a thermally, but not electrically, conductive liquid. Although rarely used for the cooling of personal computers, liquid immersion is a routine method of cooling large power distribution components such as transformers. It is also becoming popular with data centers. Personal computers cooled in this manner may not require either fans or pumps, and may be cooled exclusively by passive heat exchange between the computer hardware and the enclosure it is placed in. A heat exchanger (i.e. heater core or radiator) might still be needed though, and the piping also needs to be placed correctly. The coolant used must have sufficiently low electrical conductivity not to interfere with the normal operation of the computer. If the liquid is somewhat electrically conductive, it may cause electrical shorts between components or traces and permanently damage them. For these reasons, it is preferred that the liquid be an insulator (dielectric) and not conduct electricity. A wide variety of liquids exist for this purpose, including transformer oils, synthetic single-phase and dual phase dielectric coolants such as 3M Fluorinert or 3M Novec. Non-purpose oils, including cooking, motor and silicone oils, have been successfully used for cooling personal computers. Some fluids used in immersion cooling, especially hydrocarbon based materials such as mineral oils, cooking oils, and organic esters, may degrade some common materials used in computers such as rubbers, polyvinyl chloride (PVC), and thermal greases. Therefore it is critical to review the material compatibility of such fluids prior to use. Mineral oil in particular has been found to have negative effects on PVC and rubber-based wire insulation. Thermal pastes used to transfer heat to heatsinks from processors and graphic cards has been reported to dissolve in some liquids, however with negligible impact to cooling, unless the components were removed and operated in air. Evaporation, especially for 2-phase coolants, can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the computer's enclosure. Immersion cooling can allow for extremely low PUE values of 1.05, vs air