This pack contains 3 replacement plain foams for the Interpet PF1 filter. These foams are designed for the new PF1 filter style and should be replaced every six months to maintain a healthy, clean, and clear aquarium. The plain filter foam effectively removes particulate waste such as uneaten food or plant matter, allowing beneficial bacteria to thrive. It is easy to fit for a quick and simple filter change and is suitable for both coldwater and tropical aquariums. Please note these are the new style foams with a pre-cut hole.