This kit contains (20) 1st stage filter bags and (1) 2nd stage HEPA filter cartridge. The filter bag must be changed twice before the Bulb Eater drum is filled, and the HEPA cartridge must be changed once every 10 drums. This Combo Kit provides enough filters to trap mercury vapors from 10 full drums of crushed lamps. If you have recently purchased a Bulb Eater VRS or VRS-U from 1000Bulbs.com, you already have this kit. You will not need to buy an additional Combo Kit until you have filled 10 drums with crushed lamps.