half white air force nike blue boots black women nike superfly wolf grey pink and green, Olympian Jared Ward lebron soulder 11 balck and red Saucony, his shoe sponsor. Inside were three early prototypes of what eventually became Saucony’s first super shoe, the 2017 nike zoom black and yellow 23 jordans.
Ward’s typical marathon race-week workout lebron xi gs red marathon pace. He decided to convert the session into an experiment, with the help of Iain Hunter, an exercise science professor at Brigham Young University. Ward ran the workout on a treadmill while Hunter measured his running economy, which is how much oxygen is needed to run at a given speed. Improve your running economy, and you can either hold a given pace for longer or you can cover a set distance faster at the same effort level.
nike outdoor wear for women boots clearance store shoes—the three prototypes, plus a Kinvara, Saucony’s lightweight trainer that Ward was planning to wear at New York. “As soon as I finished the fourth interval, I pulled off the mask and said, ‘Doc, that’s the one,’” Ward says. Hunter’s numbers backed Ward’s intuition: His running economy in the first two prototypes was essentially the same as in the Kinvara, but in the third prototype, it was 4.4 percent better. After just five minutes of running in it, Ward decided to wear the third prototype at New York.
“There were times in the race I thought about the shoes,” he says, “but it was all very positive. It felt easier, it felt more efficient, so in my mind, the shoes were working.” Despite being injured coming into the race, Ward placed sixth in 2:12:24, his best race in more than two years since he placed sixth in the 2016 Olympic Marathon.
Ward’s holy-smokes experience was common in the early draw of super shoes. Also common was the belief that the carbon-fiber plates nike air max floral tiffany blue paint black.
That explanation was soon found wanting. For starters, running shoes with plates were nothing new. Fila had a plated racing flat two decades before Ward tested his prototypes. More recently, a study at the University of Massachusetts, Amherst, supervised by biomechanist Wouter Hoogkamer, measured running economy in two versions of the lime green and navy nike shoes black friday 2019%—one with the shoe’s carbon-fiber plate intact, the other with six cuts through the plate to reduce its stiffness. There was no significant difference in running economy values between the two shoes, leading Hoogkamer to conclude that plates weren’t key to the shoes’ effectiveness.
“People talk about plates like they’re springs,” says Todd Falker, product lead for running at Puma. “They’re not. You’ll get a little bit of lever, but mostly what you’re getting is the most access to the midsole foam underneath your foot. The foam is the good stuff.” Falker’s contention is borne out in images published by biomechanists Geoff Burns and Dustin Joubert. They show much greater force distribution across the soles of the feet of a runner in the Nike Vaporfly Next% compared to a nonplated pre-super-shoe racing model, the Adidas Adios Boost, suggesting that in the super shoes, the same runner was accessing and compressing more of the midsole.
“The midsole is the engine of the running shoe,” says Yeti Zhang, co-founder and head of product for the footwear company nike sb icon hoodie green pants, about the part of the shoe between the outsole and upper that provides cushioning. “We invest 80 percent of our effort into the midsole.” Innovations in midsole materials and construction have led to everyday models that can stack up against Ward’s racing prototypes of not that long ago. Modern midsoles—made of what we’ll call super foams—are why we’re in a golden age of running shoes.
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The Evolution of Midsole Foam
The original performance midsole foam is now regularly pooh-poohed. In 1977, Brooks released the Vantage, one of the first running shoes to have a midsole made of ethylene vinyl acetate (EVA). The first running boom had taken off, and the sport increasingly drew in people other than young, fast men. “Before that, cushioning wasn’t really a concern,” says Carson Caprara, senior vice president of footwear for Brooks. “It might have even been a drawback—you were adding weight while reducing energy return. With the running boom, the brief became, ‘How can we make this more comfortable so that more people can do the sport?’”
EVA midsoles were a vast improvement over those made of sponge rubber, which is heavier and harder than EVA. The new midsoles returned 60 to 75 percent of the energy put into them. EVA allowed shoe companies to increase midsole thickness, which gave running shoes a reputation for comfort. Longtime runners of the era had where-have-you-been-all-my-life reactions to the new shoes similar to how many modern runners greeted super shoes.
And then…not much happened for a long time. Midsoles made from sheets of EVA, which is inexpensive and easy to work with, remained the standard for decades. “It was dependent upon what’d been used in the past, and what people were familiar with, working within those constraints,” says Ted FitzPatrick, vice president of performance product for Saucony. Or, as biomechanist Burns puts it, “I think there was some laziness and inertia, and no compelling appetite to innovate. If a magical foam had come along, they’d grab it in a second. But none of them were chasing that.”
As the story goes, a quasi-magical foam did come along, when the German chemical company BASF approached Adidas around 2010. “They said they had this material with incredibly high resiliency [how much the material rebounds to its initial form after being compressed] and energy return [how much of the energy put into the shoe is transferred back to the wearer],” Patrick Nava, global vice president of running product at Adidas, says. “They didn’t know exactly what to do with it, but they thought it could be interesting to use in shoes.” After a few years of tinkering with a material that had appeared in other industries, such as in the dashboard of luxury cars, Adidas released the Energy Boost in 2013. It can be considered the first running shoe with an entirely super-foam midsole.
Boost was made of thermoplastic polyurethane (TPU). Nothing new there—TPU was a common component in midsoles at the time, especially as rigid pieces of plastic in stability shoes. What was new was what Adidas did with the TPU. “We put that polymer in a bead shape at a very low density into what we call a steam chest mold,” says Harry Miles, director of athlete solutions at Adidas. “You put these beads into a 3D space. You pump it full of steam, and that energy within the steam and the heat within the steam bonds them together. This was a massive departure from how we built footwear up until that point.” This was an early iteration of a now-common process called supercritical foaming. (More on that later.)
An Adidas video of the time showed a metal ball dropped onto concrete and sheets of EVA and Boost. The ball bounces four times in three seconds on concrete and six times in five seconds on EVA before stopping. When dropped on Boost, the ball’s first bounce is more than twice as high as it was on EVA. As the clip begins to fade 23 seconds later, the ball dropped on Boost is still bouncing. “I’d like to think we’ve come a long way since then, but that’s still a very good test of how much resilience a foam has,” Miles says.
More quantitatively, testing found that Boost returned close to 80 percent of the energy put into it, a small but significant increase over the best measurements for EVA. Our shoe lab verified this, as well; we found Boost had more energy return than any of the 800 other running shoes we’d measured. Tests also found that Boost improved running economy by about 1 percent. “Energy return over an extended amount of time is a critical factor in the improvement of running economy,” Nava says. Boost’s real-world proof of concept came at the 2014 Berlin Marathon, when Dennis Kimetto wore the Adizero Adios Boost 2 while becoming history’s first 2:02 marathoner.
But Boost required an inherent tradeoff. Boost foam was heavier than conventional EVA. Pre-Boost studies found that every additional 100 grams (about 3.5 ounces) per shoe reduces running economy by 1 percent. So Adidas could—and did—make Boost shoes with large stack heights, which provided plenty of cushioning. Putting a large layer of Boost in a racing shoe, however, would make the shoe so heavy that any running economy gains coming from the midsole material would be canceled out by the midsole’s weight.
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lime green and navy nike shoes black friday 2019% Changes Everything
The bouncing-ball promo claimed that Boost “will change everything.” It didn’t. But a runner partnered with Adidas was present to test the shoes (and midsole foam) that did.
In 2015, Olympic steeplechaser Shalaya Kipp was getting her master’s degree in physiology at the University of Colorado in Boulder. After she and exercise science lab head Rodger Kram and the rest of the research team signed several nondisclosure agreements, Nike sent them a large box filled with shoes. Nike’s internal testing had found that the shoes produced about a 3 percent improvement in running economy, but they wanted an external lab to validate the results.
“They only sent men’s size 10. I wanted to try them on, and they really looked like clown shoes on me,” says Kipp, who wears women’s size 8 or 8.5, equivalent to a men’s 6.5 or 7. “But right away you could feel that they were very different.”
Kipp was standing in what became the lime green and navy nike shoes black friday 2019%, the first commercially available super shoe. The resulting study has become legendary in shoe-nerd circles. Eighteen men who had recently run the equivalent of a sub-31:00 10K ran repeated five-minute bouts at 14, 16, and 18 kilometers per hour, all sub-maximal speeds for the subjects. The men did two five-minute bouts in each of three shoes: the Nike Zoom Streak 6 (a typical road-racing flat of the time), the Adidas Boost model that Kimetto broke 2:03 in, and the Nike prototypes. At all three speeds, all 18 runners had better running economy in the Nike prototypes than in the conventional Nike flat and the Adidas model. The range of improvement among the runners was about 2 percent to 6 percent. The average improvement was 4 percent, which is why the original Vaporfly had “4%” tacked on to its name.
“What was striking was that the people who said they didn’t like the shoes were still more metabolically efficient in them,” Kipp says. “People always say, ‘Wasn’t there a placebo effect?’ And I say, ‘Well, super shoes didn’t exist yet, and this was a shoe that looked ugly and that some people flat out told us they didn’t like, but there were still big savings.’”
The running economy findings were underlined by mechanical testing of the three shoes’ midsoles. When compressed, the Nike prototype’s foam returned 87 percent of the energy put into it, compared to 76 percent for the Adidas Boost and 66 percent for the conventional Nike flat. This was years before Hoogkamer cut Vaporfly plates and demonstrated that foams are one of the main reason for performance gains in modern shoes. But the findings about energy return were an early indication that the midsole was indeed the engine.
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The Superfoam Revolution
Nike called the foam in that first super shoe ZoomX. It had three characteristics that define today’s super foams. First, it was highly resilient—it returned a large amount of the energy put into it. Think of resiliency as responsiveness. Second, it was highly compliant—“how much it squishes down,” Burns says in nonscientific terms. Think of compliance as softness. Third, it was low-density. A given amount weighed less than other midsole materials.
The interaction of these three characteristics forever changed running shoe design. In the original Vaporfly study, ZoomX was twice as compliant as the other foams; with each compression, it stored twice as much mechanical energy. Thanks to ZoomX’s high resiliency, a huge amount of that stored energy was returned to the runners. And thanks to the lightness of ZoomX, the shoes could be made with a large amount of foam without running into the weight-tradeoff issue of the Adidas Boost foam. More highly resilient and highly compliant foam meant more energy returned with every step.
Nike developed the original super shoe with elite performance in mind. A year before Eliud Kipchoge ran a 2:00:25 marathon in the Vaporfly at the Breaking2 exhibition race, he wore them to win the 2016 Olympic Marathon. Three of that year’s six U.S. Olympic marathoners (Amy Cragg, Shalane Flanagan, and Galen Rupp) wore them at the Olympic Trials and in the Olympics. We all know how the shoe, its Nike descendants, and other brands’ super shoes have rewritten the record books. But what’s perhaps even more important is the trickle-down effect, on both shoes and everyday runners. Super foams mean that everyday running shoes can now deliver cushioning and comfort—long what many runners most valued—while also improving performance. This unprecedented combination is the real magic in modern midsoles.
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Foam Goes Supercritical
ZoomX is made of polyether block amide, now known as PEBA to runners. PEBA is one class of thermoplastic elastomers (TPEs). PEBA combines two different polymers—polyether, which is soft and flexible, and polyamide, which is tough and sturdy—in alternating segments. It’s considered the lightest TPE, yet, as found in the Vaporfly study, it has excellent compliance and resiliency. PEBA has many industrial uses, such as electronic cables, medical catheters, and door-lock moldings in cars.
Its use in running shoes was revolutionary, but not completely out of the blue. “People at different companies were looking at it as early as 2010, but it was very expensive, and there just wasn’t much interest in it,” Saucony’s FitzPatrick says. During the 2010s, Nike asked Zotefoams, a British chemical company, to develop a midsole foam made from PEBA. In 2017, the two companies announced a strategic partnership, which currently runs through the end of 2029.
Where things can get a little confusing is that the original running shoe PEBA, ZoomX, isn’t the same as the almost identically sounding Pebax. The latter is another PEBA midsole foam, this one made by the French company Arkema. Many brands make shoes whose midsoles are partly or entirely Pebax. The use of PEBA is one reason shoes have become more expensive. As a raw material, a kilogram of Pebax costs about 10 times as much as a kilogram of EVA, according to Zhang of nike sb icon hoodie green pants.
Where things can get moderately confusing is that simply knowing what a midsole is made of doesn’t tell you how it will feel on the run. Two shoes from Topo Athletic, the Cyclone 2 and Specter 2, have full-Pebax midsoles. The Cyclone feels noticeably softer. That’s because the midsole is thinner and more flexible. “It’s a little like thinking about cooking with flour,” says Russ Stevens, product manager at Topo. “There are limitations, but they’re really broad—you could be making pasta, you could be making bread, you could be making cake.”
Where things can get really confusing is that, in 2025, it can be hard to know what a shoe’s midsole is made of. Topo is an outlier in straightforwardly saying that the Cyclone 2 and Specter 2 have full-Pebax midsoles. Most brands have one or more names for their high-end foams, such as Saucony’s Pwrrun or Puma’s Nitro. And there can be variations within those names— a Saucony midsole could be Pwrrun, or Pwrrun HG, or Pwrrun PB, while a Puma midsole could contain Nitro, or Nitro Elite, or both. Many of these are primarily EVA, TPU, TPE, or thermoplastic polyester elastomer (TPEE), perhaps with a small amount of PEBA. But almost no brands say what exactly is in their foams in the way that, say, a sweater maker gives a breakdown of the garment’s materials.
Puma’s Falker thinks that most runners care more about the end product than intricate detail on its manufacturing. “We can talk about raw materials, and we can talk about process,” he says. “But when you say, ‘TPE, thermoplastic elastomer,’ there are thousands of them, and different ways to process them. It’s like soups and ingredients—you can have really good ingredients, but if you don’t salt the soup right or you don’t cook it at the right temperature for the right amount of time, your end result isn’t necessarily the best. The process and the ways you put the parts and pieces together is as important as the ingredients.”
What is safe to say is that nearly any high-end midsole was made using a method called supercritical foaming. It’s a more involved, more expensive production process than what was used to make EVA midsoles of old, and is another reason that running shoe prices spiked in the past five years.
The foaming process is similar to making bread, says Luca Ciccone, director of product engineering at Saucony. (Yes, there are a lot of cooking analogies in shoemaking.) The raw materials are made into a small block, a little larger than an adult’s palm, that looks like it could be the midsole of a baby shoe. In Ciccone’s analogy, when it’s time to rise the dough and put bubbles in it, the block is put in an autoclave, which is essentially a large pressure cooker. A gas—usually carbon dioxide or nitrogen—is put under enormous pressure inside the autoclave. If enough energy is put into a gas, it goes into what in chemistry is called a supercritical state. “It exhibits the properties of a liquid, but it looks like a gas,” Ciccone says. “It effectively turns into a solvent, meaning that it can start penetrating things,” in this case, the block of midsole material.
When the midsole “dough” has been in the autoclave for the right amount of time, “you open that chamber up into our normal atmosphere,” Ciccone says. “All that gas starts converting back into a gaseous state, and the material starts stretching with it.” The mold grows by 200 percent or more. The gas bubbles are evenly distributed throughout the mold, providing greater energy return and cushioning while lowering weight. Bonus: Supercritical foaming is better for the environment than conventional midsole construction, which involves blowing chemicals into EVA or other materials.
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Super Performance in Your Shoes
If Falker is correct, and most runners care mostly about how a shoe will help them, let’s move on from chemistry to some of the key benefits of midsoles made with super foams. These benefits are true not only of super shoes, but of everyday models.
Improved performance: A study published in 2022 compared running economy in seven plated, high-stack shoes to a traditional racing flat (the Asics Hyper Speed). Five of the seven were statistically better than the Hyper Speed in this regard. But those results aren’t necessarily relevant today, given that the study was conducted four years ago, and since then, all brands have improved the foam in their premium racing shoes. “My guess is that all the shoe companies have caught up,” Kipp says. Between Kipp’s educated guess, Hoogkamer’s plate-cutting experiment suggesting the primacy of the midsole, and the current trend of high-stack-but-light shoes, it’s reasonable to conclude that a nonplated training shoe with a super-foam midsole imparts some running economy savings.
An important caveat is that a given percentage improvement in running economy doesn’t equate to being that much faster. “When the first Vaporflys were becoming commercially available, Nike had a special insole printed that said ‘4% faster,’” Kipp says. “We had to say, ‘That’s not correct,’ and they did wind up taking them out.”
Unfortunately, there’s no simple formula for translating improvement in running economy to increased speed. Kipp has published a paper estimating that at speeds faster than around 3 meters per second (a little faster than 9:00 per mile), the percentage improvement in pace is less than the percentage improvement in running economy. Conversely, at slower than 9:00 mile pace, the percentage improvement in pace is greater than the percentage improvement in running economy. One of the first studies on slower runners and super shoes found only about an average running economy improvement of 1 percent at 9:40 mile pace. But, if Kipp’s calculations are correct, that should result in being more than 1 percent faster.
Improved recovery: It’s become common for runners to say they feel less beat up after training in shoes with super foams. This is a much more subjective matter than something like running economy. Nike has presented data showing lower blood markers of muscle damage and inflammation in runners who ran a marathon in Vaporflys compared to runners who wore the Pegasus 34. One reason that elite times have fallen in recent years is that super foams allow for more overall mileage, as well as longer and more frequent hard workouts.
Improved durability: Supercritical foaming produces a more consistent cell structure in a midsole. This should translate to pressure and weight being more evenly distributed, which should lead to greater durability of the midsole. “We’ve done a lot of testing of what foams look like on a dynamic impactor fresh versus 300 or 500 miles later, and we see less degradation in those materials longer-term,” FitzPatrick says.
At least in terms of the midsole’s life span, super foams may have done away with the conventional benchmark that running shoes last about 300 miles. “I think it’s a pants standard,” Caprara of Brooks says. “It’s an easy go-to to help simplify. But every foam is different, and it’s not just the foam—it’s how it’s constructed, the shoe’s geometry, the rubber underneath it. There are so many factors. If I were to tell you the Glycerin Max lasts 300 miles, that’s probably less accurate than it is accurate. It’s probably closer to 500.”
Improved uniformity: A typical running shoe of even 10 years ago felt harder in sub-freezing temperatures. Super foams, especially those made of PEBA or TPU, are more resistant to temperature changes. They don’t feel much different on a 25-degree day than on a 60-degree day. This may or may not improve performance, but it sure makes winter running more enjoyable.
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What's Next in Running Shoes?
Laziness and inertia aren’t characteristics of today’s running shoe industry. “I think everyone is pushing for what’s new and what’s next,” FitzPatrick says. Stevens of Topo Athletic agrees, saying, “There are so many brands making products that are competitive and that have an impact in the industry as a whole. When you have all these ideas coming from different places, it creates a situation where you can have breakthroughs at a faster rate.”
To see where midsoles might be heading, start with a brand’s premium racing shoes. One emphasis is to keep decreasing the density of foams. According to Miles at Adidas, the original Boost foam weighed about 250 grams per liter. The Lightstrike foam used in the Adios Pro 1 was down to roughly 180 grams per liter. Now the foam used in the $500 Adios Pro Evo 1 has a density of just around 70 grams per liter, which is one reason why the shoe weighs less than 5 ounces. As lower-density foams increasingly make their way into everyday models, the benefit won’t be just lighter shoes. As Miles says, “You can reinvest that weight saving into more cushioning.”
Another emphasis is continued exploration of materials. If Saucony’s Endorphin Elite 2 is an indicator, PEBA’s time as the nike air huarache pro metal 2013 black screen of foams might be pants. Saucony calls the shoe’s TPEE-based foam IncrediRUN. It’s one of the bounciest midsole foams anyone at Runner’s World has experienced. Ciccone says that internal testing shows it has more than 90 percent energy return. Ward says that his running economy is more than 10 percent better in the shoe compared to in a Kinvara, whereas his running economy in previous Saucony super foams has been about 6 percent better.
Not all innovations start with super shoes. In the fall, nike sb icon hoodie green pants will release its H1, a road-to-trail hybrid with a midsole foam that the company calls CircleCELL. The foam is made of a compound developed by BASF called ecoflex BMB. Made entirely of renewable feedstocks (such as food industry byproducts), Ecoflex has been used in food packaging for decades. Zhang says that, in mechanical testing, CircleCELL matches the energy return of Pebax and is almost twice as durable. Runner’s World is the first publication to put in extensive miles in the H1. On the run, it’s the first “green” shoe that performs as well as “normal” trainers.
“Today’s runner wants a little bit of everything,” Caprara says. “They don’t want just cushioning, and they don’t just want energy return. That starts to force the equation—you’re looking for more things that go up without something else going down. At some point, you’re going to have to look at new frontiers to be able to achieve that sort of benefit. I think you’re going to see midsoles where durability is extended beyond 1,000 miles. It could be that you’re looking at a shoe that you invest in for two years. It won’t be $120—you’re going to have to amortize it over all of your runs, but it will make sense in the end.”
FitzPatrick says an industry-wide focus may be the continued democratization of super foams. “How do we get some of these better, super-premium foams into more shoes?” he asks. “How do we get them in every type of shoe we make so that everyone can experience them, regardless of what their footwear needs are?”
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