When the US men’s soccer team played Ghana in Natal, Brazil yesterday, the temperature reached the mid-80s and the humidity outlook was, basically: Expect your sweat glands to sprout sweat glands. But the crazy thing about Brazil is that while it might feel like the dead of summer in one city, it could very well feel a crisp spring day in another. This unpredictability is tough enough on athletes, who ideally train in conditions that reflect the climate they’ll be competing in. But it’s also a pain in the ass for the people who design their uniforms.

The chancy weather was the main challenge Nike faced when designing the US team’s jersey for the World Cup. “It was about, how do we design against these rather different temperatures they might be facing?” says Martin Lotti, Nike’s creative director for football. The answer was loads of data points and a lot of research.

The crisp, white jersey looks pretty standard, classic even. But there are some smart data-driven design details that allow the jerseys to adapt from one temperature to another.

Before Lotti and his team started designing the jersey, they spent time with the athletes, asking them what was most crucial in a jersey for the upcoming games. “A good designer is a good listener, a good observer,” he says. “So before you put pen to paper you step back and say how has the game changed what are some data points that we can draw from?”

>Lotti and his team tested the jerseys in a simulated climate chamber, making a sweat map of the human body.

The players said they wanted to be at a stable temperature, no matter where they were playing. They also wanted the jerseys to reflect the fact that soccer has gotten faster and more dynamic. "If you look at how much faster and dynamic the game is now, you would need to put 14 players on the field instead of 11," says Lotti. "That’s how much faster and how much distance the players cover today."

Nike’s designers began by studying exactly where players sweat the most. Lotti and his team tested the jerseys in a simulated climate chamber, making a sweat map of the human body. They found that players tend to sweat the most on their back near the spine. “It’s like an inverted triangle, he says. This led him to design a similarly shaped triangle of burnout mesh. “We’re basically taking away material in the places they sweat the most,” he explains.

He also found that to increase breeziness, there needed to be a way for air to flow through the jersey more efficiently. The jersey worn in South Africa did a fine job, but Lotti wanted to make the Brazil version even lighter. Laser-cut ventilation holes line the left and right sides of the jersey, just to the edge of the ribcage and a new weave of cotton and polyester (made from recycled plastic bottles) give the tops an added breathability.

The jerseys are 16 percent lighter and have 66 percent more ventilation than the previous versions. They’re also a helluva lot slimmer. “If the game is faster you don’t want resistance and you also don’t want anyone grabbing the jerseys,” says Lotti.

The key, he says, is to make players feel like they’re almost wearing nothing at all. “It becomes more like a second skin than a jersey.”