When Adidas first launched the BOOST technology in 2013, it took the running world by storm. The energy return was high, but cushioning was better than ever and that combination formed the foundation for Adidas’ resurgence into running mainstream. From that day forward, Adidas released shoes on top of shoes on that platform, but we have seen only a little overall variance in the technology itself… if it ain’t broke, don’t mess with it is the mantra. In 2015, Adidas launches the UltraBOOST platform combining that superior midsole technology with a comfortable knit upper and builds a bridge between running and lifestyle. For 2021 we now get the sixth iteration in the UltraBOOST 21.
Quick Details, Specs, and Availability
- More BOOST than ever before, but the weight is getting a little unwieldy.
- All-new fully recycled knit upper and the return of the lace cage.
- Weighs in at 12oz or 340g for a US Men’s 9.
- Features 30.5mm of cushion and has a 10mm heel/toe drop.
- Retails at $180.00 USD and comes in 12 colors for Men and Women.
Run Test
The Adidas UltraBOOST 21 is going to feel a lot like prior iterations to people meaning Adidas has not messed too much with the overall recipe and what is expected from the UltraBOOST platform. As we mentioned, this is the sixth iteration and each one just builds up very slightly from the last. In the 21, we are getting a new upper material based on their Parley ocean plastic recycled knit as well as more BOOST than ever before. They have also added a torsion control system to the outsole to increase overall stiffness underfoot. Does this make it a better running shoe? Well, yes and no and primarily it is because of that weight.
The more we look at and run in this shoe, the more we are perplexed as to how this shoe can be 12oz for a size 9 and over 14oz for a size 12. If anything, the UltraBOOST needed to lose weight, and instead, Adidas added a plastic-based torsion control system as well as additional rubber to the outsole which drove the weight up. The additional BOOST on here also feels heavier than before, but it’s the same iteration so unclear where it’s coming from. The upper is super light, so again a lot of this leads to a heavy underfoot experience.
Now there is no debating, and happy to battle with anyone over this, that the UltraBOOST platform is incredibly comfortable. It has a nice roomy toe box, the Primeknit is soft and flexible against your foot, and that heel, even though it lacks a counter, cradles you really well. And then of course you have all that BOOST under your foot which is a nice platform that we know and love. If you liked prior versions of the ultra boost, then you will of course love the UltraBOOST 21.
As for running in them, we just can’t recommend it. This doesn’t mean it’s a bad running shoe, but Adidas has way better running shoes in their lineup that are lighter and better overall performers. The upper here is almost too roomy and it is so heavy underfoot that after a few miles, it starts to feel like you’re picking up and putting down weights. Now normally a few ounces doesn’t make for a big weight issue, but we are probably 4oz or more from a comparable shoe and that is a huge red flag for us. We would love to see an UltraBOOST that gets a much sparser outsole and see that weight come down really fast. Additionally, a structured heel counter would go a long way in terms of locking your foot in.
Bottom line, the UltraBOOST 21 is a shoe you will love to wear every day you can wear it to walk, to work, or whatever, but it’s just not great as a dedicated running shoe. We would happily grab an Adios or Supernova from Adidas before we would grab the UltraBOOST to run in. But we would grab the UltraBOOST at the drop of a hat to wear every single day for everything else, plus it looks great.
Construction: Upper
The upper is a full bootie with integrated tongue and uses their Primblue PRIMEKNIT which is composed in part of Parley ocean plastic, something Adidas has been leaning into for a while now and it is definitely a soft/plush and highly flexible material. They have brought back the plastic midfoot cage which helps with stability while also giving some structure to the shoe. The heel has no true counter and instead, Adidas has wrapped the lower part of the foot with plastic in an attempt to hold you in place. You will note the heel does extend up quite a bit and this adds a bit more comfort against the Achilles.
Beautiful Primeknit recycled upper 
Midfoot cage has returned for optimal midfoot stability 
No internal heel counter, but external support on the sides
Construction: Midsole
Adidas has added 6% more BOOST to the UltraBOOST 21 giving you just shy of 31mm of cushion on the shoe. That is it, nothing else… no plates, midfoot control, rails, etc. Just BOOST.
Midsole – lateral front 
Midsole – lateral rear 
Midsole – medial rear 
Midsole – medial front
Construction: Outsole
The outsole uses a mix of Continental rubber in the forefoot and then their rubber-based LEP Torsion System. The rubber tracks well and then the new torsion system is designed to increase stiffness overall in the forefoot, over 15% more than last year’s model, which is designed to help with overall responsiveness.
Outsole overhead- Continental rubber and torsion control
Style & Aesthetics
The UltraBOOST platform is really a lifestyle shoe that happens to be useful for running and Adidas has made that clear. This means it has great lines, looks good in every setting and by the end of the year will probably come in a ton of color options. At launch, we are getting 12 color options but our only downside is that a lot of them are in a very light color pallet so they get dirty really fast. The other color options are black based, so hoping we get some other options outside the black/white spectrum.
Overall Conclusion
The Adidas UltraBOOST 21 is a really comfortable shoe and when you have them on and are wearing them every day, it is hard to find anyone who will argue with their feel. That being said, they are really just a mediocre running shoe primarily due to their weight which is definitely 3 to 4 ounces higher than they need to be to compete in this market. Adidas also has some other amazing running specific shoes like the Adios and Supernova and we would recommend saving a beautiful shoe like the UltraBOOST 21 for lifestyle, everyday, and even work if you spend a lot of time on your feet (great for doctors and nurses).
Learn more on the Adidas website
Check Out Other Reviewers Thoughts
As always, we gather together some of our favorite reviewers so you can get a well-rounded view of the shoe. Here are our favorites.
