Genuine Intex Type S1 filter cartridge - Twelve Pack The S1 Cartridge Filter is sure to keep your PureSpa Jet Massage water clean and fresh It is made with easy-to-clean, heavy duty Dacron paper, for the ultimate filtration For maximum efficiency, clean cartridges each week and replace once a month or sooner Each filter measures 3in x 4 1/4 in Part #29001E Genuine Intex Type S1 filter cartridge - Twelve Pack The S1 Cartridge Filter (12-Pack) is sure to keep your PureSpa Jet Massage water clean and fresh. It is made with easy-to-clean, heavy duty Dacron paper, for the ultimate filtration. For maximum efficiency, clean cartridges each week and replace once a month or sooner. Replacement for all Intex PureSpa Inflatable Hot Tubs. Each filter measures 3 in x 4 1/4 in