Carbon Activated Pre-Filter 4-pack for use with the GermGuardian FLT4100 Filter E for 3-in-1 Table-Top HEPA Filter Air Purifier Model AC4100 4-Pack of Carbon Activated Pre-Filters These PreFilters are designed to fit GermGuardian FLT4100 Filter E Model AC4100 Carbon Activated filters extend the life of the hepa filter and remove common household odors Made in the USA Aftermarket product meets or exceeds OEM specs