Filter cartridges keep the water in your hot tub clean. They are easy to install and maintain. They 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. PROTECTIVE NET: The blue mesh cover protects the filter when you are bathing. This increases the life of the filter. Caution: Do not forget to remove the protective net after using the spa. Dimensions: with cover: 11cm x 8cm, without cover: 10.6cm x 6.7cm . Supplied 90 Pleats, 12 Filter Cartridges with 2 Mesh Covers.