When you walk into the San Francisco office of the cloud network and security firm Cloudflare, you’re greeted by a receptionist–and a giant wall of 100 lava lamps. It isn’t just a throwback to the 1960s. The lava lamps act as a random number generator, helping to encrypt the requests that go through Cloudflare, which make up 10% of all internet requests.

Creating randomness is an essential part of encryption because it lets you create something that an attacker won’t be able replicate. But computers themselves are actually very bad at coming up with random numbers–and that’s by design. “Computers from the beginning have been designed to very reliable, very predictable,” says Cloudflare’s CEO Matthew Prince. “When you turn them on, they always do exactly the same thing and what they’re told to do.”

So while generating randomness isn’t typically a good thing for computers–you wouldn’t want your computer to do something unexpected every time you turn it on–the patterns they rely on make the devices vulnerable to hackers. That’s where random number generators come in. To truly create random numbers, a computer has to rely on phenomena occurring outside the device itself. That could be the movement of the device in space using data from a smartphone’s accelerometer, or it could be derived from mouse movement, or the timing of a user pressing keys on a keyboard.

While Cloudflare uses industry-grade random number generators for its servers, it also decided to incorporate the backbone of its encryption into its office design. Inspired by an idea from engineers at Sun Microsystems, who thought that lava lamps could help generate randomness since modeling how fluid moves within the lamps is incredibly difficult, Prince decided to create an entire wall of lava lamps. Cloudflare calls it the “Wall of Entropy.”

Cloudflare turns the “Wall of Entropy” into encryption using a camera that photographs the wall every millisecond of every day of the year. Any one of the company’s systems can turn the display of pixels–which changes based on a multitude of factors, like the movement of the lava, the inclusion of anyone who’s walking by, and the shifting daylight–into random numbers. “Any tiny change in that photograph creates a completely random new set of inputs,” Prince says. “It’s like effectively another [die]. Because you can’t predict exactly what that wall of lava lamps looks like in any point in time, 10% of the internet is more difficult for somebody to hack or spy on.”

Throwing dice is how Prince likes to think about adding new random number generator types to Cloudflare’s mix. The lava lamp wall is another set of dice that happens to demonstrate to its customers how encryption works–and also looks great in its office. According to John Graham-Cumming, Cloudflare’s CTO, the lava lamp wall generates 16,384 bits of entropy each time it is used.