It's no secret that selling a printer—like razors or video game consoles—is a money losing proposition. Instead, it's the accessories—the blades, the games, and in this case, the inkjet cartridges—where manufacturers make most of their money.

Imagine one person's surprise, then, to discover that HP has apparently been selling its customers printer cartridges with less ink than previous models. In a post on an HP Printer Cartridges blog, user "adminsky" opened two of the same HP inkjet cartridges from different manufacturing years—one dated January 2010, and the second 2012. What he discovered was a smaller piece of hydrophobic foam inside the newer cartridge, a supposed sign that cartridges were being manufactured with less ink than what people had paid for in the past. Just to be sure, he also opened a third, different cartridge, also manufactured this year, and found an even smaller piece of foam.

To get a better sense of why this matters, we first need to examine how a typical inkjet print cartridge works. The inside of an inkjet cartridge contains a foam-filled reservoir that is mostly saturated with ink. A patent filing from Lexmark, an HP competitor, says this is typically "unfelted polyurethane open cell foam," or what we refer to as hydrophobic foam.



If you look closely at the images posted on the HP Ink Cartridge blog, you'll see that the foam is only partially saturated. "Ambient pressure is applied to ink in the foam-filled ink reservoir through the dry foam material," reads Lexmark's patent filing, and capillary action ensures that there is always fresh ink at the bottom of the reservoir. Admisnky's logic is that a smaller piece of hydrophobic foam holds "less ink for your money." However, if you look again at the cartridge teardown, it appears that the smaller foam pieces are saturated with just as much ink, if not more, when compared to the larger piece of foam, where the ink is dispersed over a wider area.

Ars reached out to HP to see whether the HP Ink Cartridge blog's assertion—that newer inkjet cartridges from the company are cheating consumers—was correct.

"It’s important to note that the size of foam inside a cartridge does not directly correlate with the amount of ink in the cartridge or the number of pages that a cartridge will be able to print," said an HP spokesperson in an e-mail earlier this afternoon.

"Over time," the e-mail continues, "the design of HP printers and ink cartridges are upgraded to make them more efficient with ink and able to deliver the same number of prints with less materials. However, the outer physical design of the cartridge has to remain the same to fit in the compatible printers." This was also pointed out in comments on Adminsky's blog and comments on other sites such as BoingBoing.



Basically, HP says it has improved the quality of its porous hydrophobic foam so that its printers can yield the same number of prints with a smaller-sized block of foam. Whether this means that the foam has been saturated with less ink is irrelevant. Instead of focusing on the amount of ink stored within a cartridge, which can actually be misleading, it makes more sense to focus on what is commonly referred to as print yield—the amount of pages that can be printed before a cartridge needs to be changed. According to HP, while the size and design of its cartridges have changed over the years, yield remains the same.

Of course, whether this is actually the case is hard to tell from pictures alone. While the size of the foam has indeed decreased, a conclusive comparison of page yield would would require a more thorough comparison between cartridges of different size and manufacture year—something which even the HP Ink Cartridge blog admits it has yet to do.

So while it's easy to believe that HP and other print manufacturers are up to something nefarious here, it seems that a piece of foam might not be the most convincing smoking gun.