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When the original Ultraboost was launched in 2015, there was nothing like it on the market. Not many running shoes were using the TPU midsole technology so when Adidas designed a full-length, 100% Boost midsole running shoe, there was a lot of excitement and hype.
The Ultraboost was not only super cushioned, very responsive and very flexible but it was so comfortable that sneakerheads started wearing the Ultraboost as a casual, lifestyle shoe.
The Ultraboost soon became the most popular Adidas running shoe because it was able to fulfill two purposes: it was a running shoe that also looked good with a casual outfit.
In a way, the Ultraboost was a pioneer and the first ever running shoe which looked good enough to be worn to the mall or out for Friday night drinks.
Over the years, the Ultraboost has kept a very similar design from iteration to iteration. This year, the Ultraboost has received a complete makeover. A new knitted upper, a new midsole with even more Boost and a brand new outsole make this the biggest Ultraboost update ever.
In the Adidas performance running range, the Ultraboost is the flagship, cushioned neutral training option. It sits above the Solarboost at the top of the range and is designed to be Adidas’ softest, max-cushioned trainer.
The new Primeknit+ upper is still a bootie construction and is even softer and more comfortable than previous versions of the Ultraboost. It has a stretchy, sock-like fit that conforms to your foot.
Primeknit + is made with Primeblue, a recycled material which is made in part with Parley Ocean Plastic. 50% of the upper is textile and 75% of the textile is Primeblue yarn.
The plastic midsole cage returns on the Ultraboost 21. Runners complained that the plastic cage was uncomfortable on previous versions of the Ultraboost but on the 21, there is one big difference: the cage is not attached to the midsole.
Instead of being glued to the midsole, the cage is stitched on to the upper and there is a gap between the cage and the midsole to allow your foot to move more freely. This setup improves midfoot lockdown while also not being as intrusive.
At the back of the shoe, a plastic heel clip is designed to keep your heel locked in place and to provide structure and support. It starts from the midfoot and extends right around the heel to the other side.
The Ultraboost 21, like all the previous versions, uses a bootie construction so it is impossible to do heel lock lacing because there are no last row double eyelets.
This means that to get a more secure foot lockdown, you have to cinch the laces very tight when tying them. It also means that heel lockdown is not as secure as in other shoes where you can do heel lock lacing.
The inside of the upper has a smooth lining and the collar is soft so it can be worn sockless or with low socks.
The fit of the Ultraboost 21 is normal in the heel and the midfoot but snug in the forefoot because of the low toe box so you might need to go up a half size if you have really wide or high volume feet.
Now on to the main part of the shoe: after all, the shoe is named after the massive amount of Boost in its midsole. This year, Boost has been increased by 6% compared to the Ultraboost 20.
The Boost in the Ultraboost 21 also feels slightly different because Adidas made it firmer in order to increase responsiveness. There is less of a plush, sink-in feeling and more of a fimer underfoot feel.
Most of the Boost is situated in the rearfoot of the Ultraboost 21 and this design makes the shoe perfect for heel strikers who need the extra foam and cushioning in the rear of the shoe to soften foot strikes.
At first glance, it looks like the entire heel is one big chunk of Boost foam but in actual fact, the sides and the rear areas of Boost are raised like rails so that your foot sits inside the midsole and not on top of it. This increases stability because there is a “cupping” sensation around your heel.
A big advantage of a TPU foam like Boost is that it is extremely durable. It's resistant to midsole creasing and it doesn't lose much cushioning over the life of the shoe.
Boost is also highly resistant to temperature swings so it won't firm up in the cold or become mushy in extremely warm climates like in Singapore.
The outsole of the Ultraboost 21 sees the biggest update from last year's shoe. Previous versions of the Ultraboost had only Continental rubber on the outsole. This year, it's a combination of hard crystal rubber and Continental.
The layout of the outsole is flat now compared to the raised lug or “pillar” design of previous versions of the Ultraboost. The result of this change is that ride transitions feel smoother.
The addition of crystal rubber firms up the ride of the shoe because of how dense the crystal rubber is. It also makes the outsole more durable because crystal rubber is more abrasion resistant than Continental rubber.
There is a plastic shank in the middle of the outsole which Adidas has named LEP (Linear Energy Push). This Torsion System is designed to make the shoe more rigid so that when flexing, it snaps back to shape quicker, increasing responsiveness.
There is a cavity under the heel that extends into the midfoot and forefoot. This is a smart way to save some weight and to help keep the foot centred during transitions.
A small amount of Continental rubber covers the toe area for extra durability. An oval island of softer rubber is situated directly under the ball of the foot so that landings don't feel too harsh.
The Ultraboost was never a shoe designed to run fast but the Ultraboost 21 changes things.
Previous versions of the Ultraboost had a soft ride which was more suited to slower runs but the changes that Adidas has made to Ultraboost 21 make it a faster shoe.
The firmer midsole, combined with the LEP System and the crystal rubber all result in a more responsive ride which has the ability to pick up the pace.
At 360g for a men’s standard size, it’s one of the heaviest shoes on the market. Heavy shoes are not a bad thing. If you get used to doing your easy runs in heavy shoes, then when you change to a lighter shoe for your tempo, speed workouts, you will be able to run much faster.
The biggest improvement to the ride of the Ultraboost 21 is how much smoother ride transitions are. The new bevelled and rounded heel design helps roll you forward and eases you through your stride.
When it comes to other max-cushioned trainers, the Ultraboost 21 rides firmer than the Nimbus 23, 1080v11, Triumph 18 and Infinity Run Flyknit 2 but it has a more stable ride than all of them and is also more durable.
The Adidas Ultraboost 21 is a medium firm, highly cushioned trainer with a very stable ride.
The new version improves on its predecessor by having a more durable outsole, smoother ride transitions and a softer, more comfortable upper.
Fans of the Ultraboost will love the Ultraboost 21. It has a more modern design and manages to improve the core features that made the Ultraboost so popular to begin with.
At $260, the Ultraboost 21 is not a cheap shoe but it's incredibly well built and capable of at least 1000 kilometres of running.
If you're looking for a do-it-all trainer that can double up as a casual, lifestyle sneaker, there is nothing better than the Ultraboost 21.