Filter cartridges keep the water in your hot tub clean. They are easy to install and maintain. They just require regular rinsing under the tap. However, if they remain dirty or discoloured after rinsing, they must be replaced. Otherwise, the filter pump may get damaged. Mspa filters are not made from paper, but polypropylene: a sign of quality and longevity. Dimensions: 11.5x8.6cm . Suitable for Hot Tub Spa collections. Only 2 Filter Cartridges Supplied.