The Puretec SF240 Shower Filter contains a redox reaction filtration media, that filters both free and combined chlorine, dirt, sediment, odours, hydrogen sulfide, iron oxides, and more, from your shower water. A redox reaction is where electrons are transferred between molecules, creating new elements. For instance, when free-chlorine comes in contact with the filtration media, it is changed into a benign, water-soluble chloride. This reaction changes free-chlorine to a larger chloride molecule. This new salt-based molecule requires more energy (heat) to evaporate than a water heater at industry-standard maximum temperatures allows and is too large to be absorbed by the skin. It is then carried harmlessly through the water supply.