Adidas UltraBoost 21 Trainers

With the UltraBoost 21 that we have tested we find a shoe that is completely oriented to the running world, with technologies, advances and features that will conquer any runner looking for comfort, cushioning and support in the same model. A pair of shoes that won’t bother you to go out every day, even on long runs, so that you can keep improving day after day, while still taking care of your feet.

The upper

The upper of these adidas UltraBoost 21 is made with Primeknit+ mesh, a fabric that prioritises support over any other feature. The German company’s engineers evolved the previous fabric, the Primeknit, to achieve more comfort and lightness in the front part thanks to the TPU molds located in that area. A kind of transparent synthetic material based on layers that is the hallmark of the German brand.

It also incorporates Primeblue technology, which, as the name itself says, is environmentally friendly. And the reason is that it is a high-performance recycled material under the seal of Parley Ocean Plastic. It consists of a thread that comes from plastic bottles and other items that we humans discard and end up ending up in the ocean. adidas collects all this plastic material to end up making Primeblue to keep the seas and oceans cleaner. It is worth noting that this initiative was launched in 2015 and since then has managed to recover tons and tons of plastic to make trainers, clothes and other accessories.

Finally, it has a very thin tongue that is also really comfortable and is fully integrated into the upper. This minimises the chances of movement or discomfort.

The midsole

The adidas Ultraboost 21 couldn’t have any other midsole than the brand’s exclusive Boost technology. They only have the Boost, although in this 21st edition the percentage of foam has been increased compared to previous versions. According to the German brand, it contains 6% more Boost than its predecessor making the reactivity even greater but also the protection of our joints, since the impact absorption will be more controlled dissipating even better the forces throughout the length and width of our foot.

But one of the main disadvantages of having more Boost and wider midsole is that it affects the weight. In our case, a 9,5US, the adidas UltraBoost 21 weighs a whopping 348g. A really high weight for an asphalt shoe.

If we look at them from the side, we can see how the geometry, the dimensions of these shoes have changed a lot compared to the 20th edition. The heel has a very pronounced bevel and a large amount of Boost. A quantity that is not vertically in its entirety, but is distributed laterally to achieve a greater amplitude of the sole in order to increase stability and avoid the occasional twist. Unlike other comparable running shoes, these UltraBoost 21 don’t have a midsole plate. They don’t need it, because with the Boost technology you get a great reactivity and a very fluid transition -we’ll talk about how to wear them in its corresponding section-. However, between the midsole and the outsole it incorporates a portion of yellow plate that helps to a better fluidity, but without being carbon. adidas calls it L.E.P. We will see it more later.

This is what the sole looks like

The outsole of the adidas UltraBoost 21 is another part that has received major changes compared to the previous edition. Based on StretchWeb technology with Continental rubber compound, it features a new geometry with a protected perimeter and a central area in the forefoot to increase traction during toe-off.

We can see that it has 3 distinct areas in different colours:

On one side we have the translucent area, the same as the pink area. In both parts it is a crystallised rubber from Continental that follows the entire contour of the shoe. Some areas that will receive more wear given the position. It is also the material that will ensure that the TPU piece that forms the L.E.P. is not damaged.

And what is the L.E.P? It is a piece of thermoplastic polyurethane in the shape of a yellow X that replaces the classic Torsion system of the German company used by the previous Ultraboost. Linear Energy Push (L.E.P) is thicker and stiffer than Torsion which provides more stability and longitudinal stiffness.

The other area is the kind of central islet, surrounded only by Boost. As we have already mentioned, it still uses the Continental in the outsole with which we can expect an excellent grip in any of the weather conditions we face. Whether the terrain is wet or dry, it is synonymous with confidence. Guaranteed! But it is also synonymous with durability, even though we can dig our nails in and imagine that in no time we will no longer have a sole.

Putting in the miles

You may think that the upper material of this adidas UltraBoost 21, since it requires several processes, is less comfortable than others. Wrong! You mustn’t think like that. Thanks to the process of transforming recycled plastic into yarn, Primeknit+ is as elastic as the original Primeknit. You won’t even know the difference.

The fit of the upper of these adidas UltraBoost21 is very nice, they fit like a glove and the sensation when wearing them is like a second sock. They are perfectly tucked in as well as offering great breathability thanks to the number of holes in the toecap (the yellow part) and sides.

At first they seemed a bit hard. Maybe because we were coming from a softer cushioning or maybe because we are light runners for this model. But after a few rides we started to feel it totally different.

The Boost just got nicer. Even more reactive. More effective.

The transition in these adidas UltraBoost 21 is very smooth and continuous. They offer a really energetic response on impact with the heel to move towards toe-off. Especially when the forefoot part comes into play, which is more dynamic than the heel part despite not being as cushioned. In any case, they don’t lack cushioning in this area.

If we focus on the behaviour of the Continental outsole, the shoes don’t slip or anything like that, even if you go through wet or slightly wet areas. It has excellent behaviour in any condition we face. In our case we haven’t tested it in areas with dirt or rocks, because we have other kind of shoes for that and we believe that nobody who has an adidas UltraBoost will run in those areas. If they could be tested on athletics tracks, with tartan, but being a slightly rougher surface, surely the grip is much better. As for the durability of the outsole, we give it a very good score. After several weeks of testing doing around 50kms per week, the sole seems new. No signs of wear. 


The adidas Ultraboost 21 was a shoe we were really looking forward to after the excellent marketing of the German brand. And the result has been pleasantly surprising for its good performance despite the fact that at first glance we were a bit surprised to see so much midsole.

This is a shoe that is easy to go out and ride in thanks to the Boost effect, the smooth transition, the nice support and comfort for our feet and the excellent traction they offer.

In short, the adidas UltraBoost 21 is a shoe that will make any road runner be able to adapt perfectly to them. It should be noted that the heavier the runner, the greater the benefits of the Boost.

For who?

The adidas UltraBoost 21 is a shoe for heavier runners, men over 80kg and women over 65kg, with a neutral/supinator stride who want a shoe for relaxed running or active recovery. Perfect for running distances from 10kms up to half marathon at paces above 5’00/km.


Boost cushioning





Tightness of the last

Technical information:

Brand: adidas

Model UltraBoost 21

Fit system: Lace-up

Upper: Primeblue and Primeknit+

Midsole: Boost

Sole: Stretchweb with Continental rubber compound

Drop: 10 mm -20,5mm toe and 30,5mm heel-

Available sizes: 36EU to 52 and 2/3EU

Weight: 348g in size 9,5US

Colours available White/Green/Black; Navy Blue; White; Orange/Grey; Black; Black; Black/Grey

More information here

Test: Adidas UltraBoost 21 Trainers
Adidas UltraBoost 21 Trainers With the UltraBoost 21 that we have tested we find a shoe that is completely oriented to the running world, with technologies, advances and features that will conquer any runner looking for comfort, cushion …
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Test: Adidas UltraBoost 21 Trainers

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