When Google announced Project Loon in June of last year many balloon experts were skeptical of its chances. The stated goal was that the balloons that would last 100 days or more in the air, but nobody was routinely getting anywhere near that kind of longevity. Much larger NASA balloons typically stayed in flight for less than 60 days. Google was aiming to nearly double that, and at a much lower cost. "Absolutely impossible—just talk to anybody in the scientific community," veteran balloonist Per Lindstrand told Wired. "Even three weeks is very rare."

100 days aloft is now commonplace

Today, Google is announcing a number of achievements, the most important of which it's dubbed The Marathoner, a balloon launched in July from New Zealand that came back to Earth in Chile 134 days later. "When we started out, 10 days was an achievement. Then we hit 30, then 70 and now it is commonplace for us to get into the 100 day realm," said Mahesh Krishnaswamy, who leads Project Loon’s manufacturing efforts.

That durability is the result of intensive testing, including one peculiar late night revelation. "Even a tiny hole, say 2millimeters, can take weeks off the lifespan of the balloon. And trying to find a 2mm hole on a balloon with a surface area of 600 square meters is like looking for a needle in a haystack," says Krishnaswamy. "I was trying to figure out ways to test for leaks, and suddenly, in the middle of the night, it came to me. Condoms!"

Trying to create an unbroken ring around the globe

Krishnaswamy and his team adopted liquid and electrostatic tests used by the condom industry to test for microscopic leaks. That led them to new materials and changes in the structure of the balloons that have significantly extended their lifespan, bringing Project Loon closer to its goal of creating an unbroken ring that extends around the globe, a circle of floating cell towers that would be able to provide uninterrupted Wi-Fi with speeds that have reached 10MB down in recent tests.

Along with The Marathoner, Project Loon is highlighting a few other notable balloons. The Sprint Star title goes to the fastest Loon balloon, which traveled 324 kilometers per hour while rushing to the South Pacific Ocean over Antarctica. The Frosty Survivor endured temperatures of -83°C (-117°F). "The weather is tough, because the balloons can get very brittle," says Krishnaswamy. Rapid temperature shifts as the balloon ascends and descends cause it to contract and expand. "Imagine a rubber band you put in the deep freeze and then try to stretch. Snap!"