Activated carbon filters used in hydroponic grow rooms are the most effective means of cleansing the extracted air to remove any odours. These filters work by a method called adsorption (as opposed to absorption). Simply put, adsorption means that odour-causing molecules stick to the inside of the activated carbon without the carbon itself increasing in size. In the same way that a sponge can only hold so much water before it is completely saturated, carbon filters to reach a point where they are unable to extract any further odour-causing molecules from the air. In addition, the adsorption characteristic of the carbon means that heavier molecules can displace lighter ones – freeing the lighter molecules to flow out into the atmosphere. For growers, this means that they will detect odours leaving their extraction ducting before the filter reaches the end of its useful life. This is known as the breakthrough point.