The Adidas Ultraboost, one of the most consequential shoe styles of the last two decades, just got an update with the Ultraboost 21 (available starting today for $180 from adidas.com, with wide release on February 4). A masterful mix of performance tech and hypebeast-worthy design, the original silhouette helped to drive Adidas to the forefront of the sneaker world by putting the company’s innovative Boost foam, which helped to spark an energy return revolution in the running shoe world, into a housing that appealed to street style aficionados.
The OG Ultraboosts are one of my favorite pairs to wear—they fit just right, providing incredible cushioning and a nice spring to my step as I stride around the city, all while looking fresh paired with everything from sweats to slacks. As much as I enjoy wearing these shoes in my day-to-day life, however, they’re not exactly my first choice when I lace up for a run.
While Boost was the first big name in energy return foam, I personally feel like I’m running on an overly soft surface when I’m wearing Ultraboosts, which throws off my stride and leaves me wishing for firmer footing. I’ve come to prefer carbon plate shoes, like Adidas’ excellent Adizero Adios Pro or the Nike Air Zoom Alphafly Next% for speed days and races, or kicks with firmer foam for laid back runs instead.
How the Ultraboost 21 Feels on a Run
So when I first laced up the fully redesigned Ultraboost 21, I was skeptical about running performance. But then I took my first few strides and was very pleasantly surprised. While the skintight, sock-like fit was familiar from wearing the line’s previous entries, my feet weren’t so cushioned that I struggled driving through my full stride. In fact, I felt more like I was propelled into each following step, making my runs feel more effortless. The Boost foam both provided comfort to absorb contact and a peppy bounce, while my feet felt just as light on the last few steps of the run as they did when I started. This was a pair of shoes I could see myself wearing for miles.
The key to the Ultraboost 21’s performance is in just how radically it’s been redesigned. The line has seen some changes before, with tweaks (namely adding more Boost material and a cutaway heel frame) for the 19 and 20 variants, but the updates haven’t been as visually striking as the 21. The shoe retains the most recognizable features of the line—the stretchy Primeknit upper, Boost foam, torsion element in the midsole, and Continental Rubber outsole—but blows up the midsole with its maximalist take on Boost. The heel frame is gone, and the foam stack is visibly much higher than before.
Adidas increased the amount of foam in the midsole by six percent from the previous iteration.
That doesn’t sound like a whole lot more material—but the difference is striking when you compare the OG to the 21 side by side (or heel to heel, as I did when I was checking out the shoes for the first time).
How the Ultraboost 21 Was Redesigned
This wasn’t just a random amount of material, according to Adidas Global Director of Footwear Stephan Scholten. That six percent number was the result of the design team’s process of trial and error to find a balance between what he refers to as the two “contradictory elements” that make the Ultraboost line special: comfort and responsiveness.
“We said okay, let’s look at what is the sweet spot that we can still improve or increase the Boost percentage in the midsole without creating a kind of wobbly or not great running experience,” he says. This is a fine line to tread; some of my favorite shoes for running are not great to walk in, since I have to balance on their high foam stacks. Thankfully for any casual Ultraboost fans, this isn’t the case here. The 21s have become one of my go-to pairs of dog walking kicks because they’re so easy for casual strolling (although I have a tough time keeping my excitable pitbull from scuffing up the clean white and neon colorway with her paws).
But the feel of the shoe on the road—the sense of being propelled in my experience or responsiveness, in Scholten’s parlance—is as much a product of the new torsion system, which the brand calls the Linear Energy Push (LEP) system, which sits beneath the Boost midsole. Adidas says the unit results in a 15 percent increase in forefoot bending stiffness from previous iterations of the Ultraboost line.
I would compare the sensation to how I’ve felt when wearing shoes from Nike or Hoka One One that use a rocker shape to move the runner forward through the toe-off portion of the stride. But that’s not quite a one-to-one comparison, according Scholten.
“[The Ultraboost 21] doesn’t rock you forward. It really propels you forward,” he says, comparing the performance goals of the Ultraboost 21 to the carbon plate Adizero Adios Pro. “Biomechanically, what we are trying to do in the Adios Pro is to increase ease and to decrease concentric and eccentric work to have a higher biomechanical advantage or ergonomical advantage. Whereas on the Ultraboost, we really tried to increase the concentric work—you feel this forward push in the last phase of your of your transition, really, so you really go from one step to the other, and you get propelled forward.”
In non-shoe nerd speak, the Ultraboost 21 is built to feel spring-loaded and super comfortable at the same time.
The Ultraboost 21 as a Style Staple
The 21 performs well, but other high-end running shoes don’t have to carry on the Ultraboost’s unique style legacy. The first photos of the 21 looked a bit strange to me–I could see how the performance details might work, sure, but I wasn’t sure if the high foam stack would translate for the jogger and oversized jacket crowd.
In person, though, the Ultraboost 21 has the look of a true Ultraboost 1.0 successor that the last two iterations, with their chunky heel cutouts and built-up lace cages, lacked. According to Scholten, that was the point. “What we really try to do with the Ultraboost now was to take the ingredients that feels familiar for the people that love the very first Ultraboost,” he says. “So when you look at the T-toe, when you look at like the cage–it just feels a bit more Ultraboost 1.0. But what we have then done is have taken all the learnings, all the insights, all the innovation, and just transfer that six years later down the line.”
I can see that throughline, especially looking at the shoes next to one another. Now, I just need to get a Triple-Black version of the 21, and I can really combine the top line performance with top line style.
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