HUMAN beings are bags of brine. This presents a problem for wireless communications, because the range of most commonly used radio frequencies lose signal strength when passing through salt water, as well as through masses of fat, muscle and bone. In large public spaces, like an open area at an airport terminal, human bodies are spread out and have little effect compared to the building materials that enclose the space, like metal and sheet rock. Even in a house, brick and chicken wire are much worse than people in reducing the range of a network. But on an aircraft, even a partially filled cabin provides lots of opportunities for wireless signals to be sucked into folds of flesh.

Human bodies exhibit the dielectric effect, acting as a strong insulator for electromagnetic fields passing through them, such as wireless networking transmissions. The mix of water and salts in a human body are particularly good at attenuating signals in the separate 2.4GHz and 5.0GHz ranges used for Wi-Fi networks worldwide. (This is also true of the varied parts of the 700MHz-3.5GHz range used for mobiles worldwide.) Wi-Fi is already in use aboard more than 1,600 planes that fly over the United States, so the problem is no longer academic. Companies that install Wi-Fi and mobile kit for customers, including Boeing, its European rival, Airbus, an American provider of in-flight Wi-Fi called Gogo and the satellite-based mobile operator OnAir, have had to work with this constraint for years.

But until recently, firms had to use a combination of computer modeling and human testing in labs and cabins to simulate different conditions to determine where to design and position antennas. It was expensive, time consuming and imprecise. Herding hundreds of stand-in passengers into a prototype plane was one solution, but neither practical nor comfortable to the subjects. So Boeing has come up with another, in the form of sacks of spuds. To prove that this is not an early April fools jape, Boeing has even produced a video, and a bunch of experts, explaining the approach. Potatoes, it turns out, affect the a Wi-Fi signal in much the same way people do.

The Synthetic Personnel Using Dielectric Substitution—or SPUDS—project mimicked human bodies using 9,000kg (20,000 pounds) of tubers. These were easier, and significantly cheaper, to push around than people would have been. Boeing also says this enables far more rapid testing without any loss of accuracy. Once the tests were successfully completed the company donated the vegetables to a local food bank.