These special revisions of the HP 304XL ink cartridges have been designed to work with the most recent HP firmware. When producing these remanufactured Hewlett Packard cartridges they have focused specifically on the Deskjet and Envy printers listed as compatible, that we were previously unable to offer cartridges for.Remanufactured Hewlett Packard ink cartridges like the HP 304XL multipack found here, retain as much print quality as possible and lessen the environmental impact of your printing. All the genuine Hewlett Packard mechanical parts are retained and the empty cartridges are then refilled with a top-quality HP 304XL black, cyan, magenta and yellow ink. The completed remanufactured HP 304XL ink cartridges are then thoroughly tested by our manufacturers. The attention given to the HP 304XL units during refilling means they remain compatible with all the same thermal inkjet printers including the HP Deskjet 3720 and HP DeskJet 3730. Like all our products, the remanufactured HP 304XL ink cartridge valuepack comes fully guaranteed and is covered by our 100% satisfaction guarantee.