The HP DesignJet T850, T950 and T870, including the T850 MFP and T950 MFP, with the HP 739 printhead. The older T730 and T830 use HP 728 ink instead, and the two ranges are not interchangeable.

They are water-resistant rather than fully waterproof. Because all four inks are HP Flex Tech pigment inks, a water drop or spill will not make the lines run, and prints resist smudging and highlighter bleed. That makes them a good choice for drawings taken to site.

Yes. A 300 ml cartridge holds 2.3 times the ink of a 130 ml cartridge for about twice the price, so it costs less per ml and needs changing less often. Buy 300 ml for the colour you use most, usually black for CAD line work, and 130 ml for the others.

Original HP cartridges are covered until the ink runs out or the warranty-end date printed on the cartridge, whichever comes first. HP's printer warranty does not cover damage or repairs caused by non-HP, refilled or expired cartridges, so genuine ink also protects the printhead and the plotter itself.