Cabin microfilters don't affect the performance or longevity of your engine, but an old and dirty cabin filter can impact your health. The microfilter removes contaminates that enter the heating and air conditioning vents, but over time it can become full of dirt and dust, with mould potentially growing if there's any moisture in the system. Replacing the cabin filter is part of the maintenance schedule, but is too often overlooked. We recommend replacing your cabin filter if there's an odour emanating from the vents, or you find yourself sneezing when you turn the fan on. Manufactured by BMW supplier MANN, this pair of microfilters has been impregnated with charcoal for greater filtration.