Sneaker rivals race to find the next super foam

The New Balance 990 running sneaker had earned mass appeal in its four decades on the market. So when designers at the Boston footwear company considered injecting the shoe with a squishy foam that boosted the midsole by about 2 millimeters, they faced resistance.

“Hotly debated,” New Balance vice president of global footwear design Brad Lacey said of the late 2022 move, which some inside the company feared would alienate the running shoe’s devoted following of people who don’t run.

It didn’t. Cushioning technologies such as New Balance’s FuelCell—a high rebound foam built for racing that will be worn by athletes at the Paris Olympics this summer—have fueled record sales at New Balance and seeped into every corner of the running sneaker market.

Executives across the footwear industry say postpandemic shoppers are more concerned with comfort, even now that many of them are back in the office. Companies from upstarts such as On and Hoka to more established names such as New Balance and Under Armour are fighting for supremacy in a new era of bulky running shoes.

The battle has been playing out inside research laboratories where scientists use machinery to test and tinker with foam compounds developed by chemical companies that are better known for creating plexiglass, working with NASA or making car seats.

“You’ve had a couple of sparks and now the whole market has moved there,” said Kyle Blakely, vice president of innovation at Under Armour.

Cushioning was always a priority for running shoes. But in the past companies balanced it against factors like stability, durability or weight. That changed about a decade ago when Hoka went all in on foam.

The Deckers Outdoor-owned company gradually built a following of avid runners. Then something clicked. Everyday sneaker wearers took to the chunky look. Sales of Hoka reached $1.8 billion for the year ended March 31, compared with $352 million in 2020.

As companies warmed to the idea that they didn’t have to sacrifice fashion for foam, the race was on. Zurich-based On teamed up with Arkema, a French chemical conglomerate that developed a compound known as PEBAX that is used in the brand’s Helion foam. Nike has leaned on British Zotefoams, which provided the material used for the midsole of one of the first super shoes, Nike’s Vaporfly. Dow Chemical is behind the foam used in Under Armour’s Flow technology, used by NBA star Stephen Curry.

Super shoes, designed mostly to maximize performance in races, were popularized in 2017 after Nike’s attempt to stage a sub-two-hour marathon. The shoes are usually made up of a thick layer of super light foam and a rigid plate, often made of carbon fiber. Most companies now have a super shoe that runners will wear for road races and other tiers of running shoes that are worn for training.

Industry executives say they are driven by athletic performance, not on catering to the fashion tastes of the masses. “If we see that there’s a use case in other communities, then this is an amazing side effect,” said Ilmarin Heitz, On’s senior director of innovation.

Shoppers want performance features along with versatility, said Kevin Fitzpatrick, New Balance’s vice president of running. “Very few people are actually buying that shoe to just go out and run in it,” he said about the 990.

Executives say the current change in midsole thickness is part of a common, though largely unacknowledged, effort by shoe makers to straddle the line between performance products and everyday wear. To meet rising consumer interest in trail running, companies are releasing new versions of their hiking and trail footwear. The trend has already crossed over to fashion as part of an increasingly popular style known as gorpcore—said to be named after the acronym for trail mix that is short for “good ol’ raisins and peanuts.”

Under Armour’s Proving Grounds is filled with ex-athletes who wear white lab coats. In the climate controlled-room, inside the company’s 35,000-square foot innovation and manufacturing center in Baltimore, scientists test the limits of materials that might make it onto its latest products.

The athletic company tried about a dozen compounds from different vendors, controlling for climate and other conditions, before choosing a beaded foam for the company’s new Infinite Elite running shoe.

The idea for the Infinite Elite was to create a shoe that would be all about sustained comfort for long runs. Runners training for a marathon can typically wear out a pair of running shoes in just over a month. At about $160 a pair, it is a big investment for the consumer and a big opportunity for the brand, said Bradford Eagan, Under Armour’s materials engineering lab manager.

“If you can get the trust of that athlete you’re going to have a buddy for life,” said Eagan, who ran track for Marquette University.

Eagan and his team developed different methodologies to quantify the fatigue and durability of the foam to make sure the material feels the same way throughout the entire run. Scientists take foam slabs that measure about 4 inches and put them through a gravity-driven impact attenuation instrument, a hydraulic press-like machine that can hit the foam with the force of a 155-pound athlete running a seven-minute mile. Most companies in the footwear industry use similar machines.

The foams used for running shoes act as a pillowy spring, soft on the feet and returning energy with every stride. When it comes down to cushioning, footwear companies generally use one of several basic chemical compounds.

While the components of a running shoe are generally the same, variations in stack height, the rocker angle, geometry and other factors make each model its own unique system.

“You can start with the same eggs, and you can make lots of different omelets,” said Tony Bignell, Nike’s vice president of running footwear. “Otherwise all shoes would feel the same way.”

Nike recently unveiled a host of new products for the Paris Olympics featuring a combination of its proprietary air bubble technology, Zoom Air, with a PEBA-based foam.

Chemical companies can tweak the compounds and manufacturing processes to get similar results. If one innovates, the rest can soon follow. Zotefoams was among the first to infuse a foam with nitrogen and helped Nike develop its ZoomX foam technology. Now other companies such as Under Armour and New Balance have also used nitrogen in their own way. The brands say their scientists will work with the chemical companies and request adjustments to the foams, making the cushioning proprietary in the process.

“Most of the brands, they use just foam but tweak it as much as they can,” said On’s Heitz. “Our winning piece is basically how we put it together.”

Executives know that some foams don’t have a long shelf life. Runners can tear through a pair of shoes quickly, and some foams don’t feel the same way after a few hundred miles. There is still a lot of room for improvement in terms of durability and sustainability, but at some point everyone is going to be squeezing blood from a stone, Under Armour’s Blakely said.

Under Armour is looking for new polymer sets for new foams, new methods of making the foams and new shape modifications.

They are also looking beyond foam. “That’s the real frontier,” Blakely said.

Write to Inti Pacheco at inti.pacheco@wsj.com