Our verdict

The Nike InfinityRN 4 distinctively differentiates itself from its previous model. Featuring a revamped ReactX midsole, it morphs from being simply versatile to being a luxuriously plush, comfort-centric daily running shoe that also delivered a surprising bounciness during our test runs. Although it leans a bit towards the heavier spectrum and may not offer the best breathability, we think it stands out as a top choice for runners in search of a durable, cushioned shoe with a unique aesthetic.

Pros

  • All-new ReactX plush midsole
  • Soft and stretchy Flyknit upper
  • Ideal for heel strikers
  • Generously cushioned
  • Excellent for easy runs
  • Feels like running on clouds
  • Durable, long-lasting outsole
  • Reduced carbon footprint

Cons

  • Average-at-best breathability
  • On the heavier side
  • Sizes run notably small

Audience verdict

85
Good!
  • Top 24% most popular running shoes

Who should buy

The Nike InfinityRN 4 gets our seal of approval for:

  • Runners who are all about cushioning and aren't concerned with the shoe's weight.
  • Marathoners looking for a comfortable pair for easy or moderate runs.
  • Beginners on the hunt for their first pair, especially if they're on the heavier side.

Nike InfinityRN 4

Who should NOT buy

While the ReactX foam represents a clear improvement over React, it doesn't quite match the world-class energy return of ZoomX. If performance and bounce are what you're after, we think that the Nike Invincible 3 offers a similar concept and design, but with a full ZoomX midsole.

Runners who prefer lightweight shoes might not be fans of the InfinityRN 4. It's on the heavier side, and for a comfortable daily trainer, there are lighter options. We recommend considering the ASICS Cumulus 25 or the New Balance Fresh Foam X 1080 v12, both of which deliver similar features in a lighter package.

Nike InfinityRN 4 parts

Breathability

Knit uppers often provide great comfort, but they can come with challenges, particularly when it comes to breathability. We discovered that the Nike InfinityRN 4 falls into this category.

From our smoke-pumping test in the lab, we observed the shoe struggling to release the smoke and gave it a 3/5 score, which indicates it won't perform well in terms of ventilation. We'd advise against using them for hot summer runs.

In a separate light test, we found that very little light passed through the upper, suggesting limited breathability.

It's clear that Nike prioritised comfort with this model. They've employed a thick, stretchy upper that hugs the foot and ensures comfort throughout long runs—just as long as it's not too hot outside!

Nike InfinityRN 4 microscope

Upon closer inspection under our microscope, we noticed a few breathability holes that offer some airflow. Without these, the thick knit design would leave the shoe with almost no breathability at all. Thankfully, there's at least a bit of ventilation.

Nike InfinityRN 4 microscope 2

Test results
InfinityRN 4 3
Average 3.8
Compared to 226 running shoes
Number of shoes
1
Breathability
5

Durability

Toebox durability

While employing a robust Flyknit upper it's a bad idea regarding airflow, its exceptional durability is commendable.

We've found that the InfinityRN 4, with its impressive 4/5 rating, truly shines in our Dremel test when compared to almost any other road running shoe.

Nike InfinityRN 4 Toebox durability
Test results
InfinityRN 4 4
Average 2.4
Compared to 160 running shoes
Number of shoes
1
Toebox durability
5

Heel padding durability

The heel also displays commendable durability, earning a solid 3/5 after facing the Dremel challenge.

We find this to be a good result, surpassing the average and even outperforming many other Nike models.

Nike InfinityRN 4 Heel padding durability
Test results
InfinityRN 4 3
Average 3.1
Compared to 156 running shoes
Number of shoes
1
Heel padding durability
5

Outsole hardness

Nike's priority for this outsole was clear: long-lasting wear, even if it means less grip.

Nike InfinityRN 4 outsole

The outsole is designed with numerous cutouts, enhancing both its lightness and flexibility.

With the InfinityRN 4, they've incorporated a 90.4 HC outsole—one of the hardest we've ever measured in our lab.

Nike InfinityRN 4 Outsole hardness
Test results
InfinityRN 4 90.4 HC
Average 80.5 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 277 running shoes
Number of shoes
54.9 HC
Outsole hardness
92.8 HC

Outsole durability

The tough rubber Nike uses really shows its strength. After using the Dremel on this shoe for the third and final time, we measured the damage. The indentation was a mere 0.3 mm! 

That's an impressive result. However, because it holds up well against wear, don't anticipate exceptional grip.

Nike InfinityRN 4 Outsole durability
Test results
InfinityRN 4 0.3 mm
Average 0.9 mm
Compared to 138 running shoes
Number of shoes
0.0 mm
Outsole wear
2.0 mm

Outsole thickness

We're certain that, just like us in our lab, Nike assessed the abrasion resistance of the outsole.

Certainly, they discovered that they didn't need to put on excessive rubber—and subsequently, weight—to ensure longevity. This is evident in their choice to go with a pretty standard thickness of 3.7 mm.

Nike InfinityRN 4 Outsole thickness
Test results
InfinityRN 4 3.7 mm
Average 3.2 mm
Compared to 296 running shoes
Number of shoes
0.0 mm
Outsole thickness
6.6 mm

Weight

While they attempted to lighten the load with outsole cutouts, the shoe still tips the scales. Weighing in at 11.1 oz (316g), it's undeniably on the heavier side.

To put things in perspective, the ASICS Superblast manages to be 2.7 oz lighter even with a higher stack height.

Nike InfinityRN 4 Weight
Test results
InfinityRN 4 11.15 oz (316g)
Average 9.35 oz (265g)
Compared to 297 running shoes
Number of shoes
5.26 oz (149g)
Weight
12.56 oz (356g)

Cushioning

Heel stack

Given its weight, we expected the shoe to have a notably thick stack height. However, we discovered that it's actually quite average.

A couple of years ago, 34.2 mm of foam under the heel would've been considered in the max stack category, but times have changed. As Dylan sang, "The times they are a-changin'."

Nike InfinityRN 4 Heel stack
Test results
InfinityRN 4 34.2 mm
Average 33.6 mm
Compared to 296 running shoes
Number of shoes
7.6 mm
Heel stack
42.7 mm

Forefoot stack

In the forefoot, we measured a typical thickness of 24.4 mm.

Nike InfinityRN 4 forefoot

We found that this provides enough cushioning for any runner. It makes this shoe a reliable choice even for long runs.

Nike InfinityRN 4 Forefoot stack
Test results
InfinityRN 4 24.4 mm
Average 25.0 mm
Compared to 296 running shoes
Number of shoes
7.6 mm
Forefoot stack
35.8 mm

Drop

While Nike lists this shoe with a 9 mm drop, we measured it in the lab at 9.8 mm. This slight difference is within an acceptable range.

With 9.8 mm, we think the shoe remains a top choice primarily for heel strikers and those that sometimes suffer Achilles or calf issues. That said, midfoot and forefoot strikers can also comfortably wear it, although they might benefit more from a lower-drop daily trainer like the Hoka Clifton 9.

Nike InfinityRN 4 Drop
Test results
InfinityRN 4 9.8 mm
Average 8.6 mm
Compared to 296 running shoes
Number of shoes
-0.8 mm
Drop
16.1 mm

Insole thickness

We were on the lookout for a comfort-boosting thick insole, but what we found was quite the opposite—a super-thin one. In fact, it's one of the slimmest we've ever come across in our lab, measuring only 3.1 mm!

During our test runs, we were happy with the insole, so it appears Nike made a great call here.

Nike InfinityRN 4 Insole thickness
Test results
InfinityRN 4 3.1 mm
Average 4.5 mm
Compared to 292 running shoes
Number of shoes
1.5 mm
Insole thickness
7.3 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

The biggest update from the Nike React Infinity Run Flyknit 3—apart from its shorter name—is the foam. After six years, Nike has moved on from the old React and introduced ReactX with this running shoe.

Observe how the foam is shaped to enhance compression toward the heel.

ReactX is a more responsive and softer variant of the original React. Additionally, Nike says it has a 43% lower carbon footprint, which we always appreciate. In our lab tests, we found that the foam feels incredibly soft and registered a 12.5 HA on our durometer—20% softer than the v3.

Nike InfinityRN 4 Midsole softness
Test results
InfinityRN 4 12.5 HA
Average 21.5 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 224 running shoes
Number of shoes
8.5 HA
Midsole softness (soft to firm)
41.5 HA

Difference in midsole softness in cold

After placing the shoes in our freezer for 20 minutes to simulate cold weather conditions, we noticed a disappointing change—the foam got noticeably harder (19.0 HA).

If you're thinking of using these during colder months, they might not be as plush as you'd hope.

There's a staggering 52% difference between the two tests. This happens because ReactX it's still a mix of TPE and EVA. Sadly, this means the foam doesn't hold up well in cold temperatures.

Nike InfinityRN 4 Midsole softness in cold
Test results
InfinityRN 4 52%
Average 25.6%
Compared to 223 running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Stability

Lateral stability test

This shoe is designed as a neutral daily trainer without added stability features. So, given the plush midsole, we didn't anticipate exceptional stability.

Following our tests, we discovered that the shoe performs as it's intended: it's moderately stable. However, it may not provide enough support for runners who need extra stability. For those runners, we'd recommend looking into the ASICS Kayano 30.

Torsional rigidity

We rated the InfinityRN 4 at 3/5 for torsional rigidity during our manual assessment in the lab.

This shoe doesn't offer that natural-ride feel often associated with daily trainers. If you're after a shoe that you can twist without any issue and gives a more natural feel, consider the Saucony Ride 16.

Test results
InfinityRN 4 3
Average 3.2
Compared to 275 running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

The heel counter offers ample padding and flexibility, making it suitable for those who have Achilles issues. We gave it a rating of 2/5 in our evaluation.

Test results
InfinityRN 4 2
Average 2.8
Compared to 259 running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

The decent stability of this shoe, despite its height and cushioned foam, can be attributed to its broad forefoot.

Nike InfinityRN 4 forefoot

Measuring at 118.4 mm, we discovered that it ranks among the widest running shoes we've evaluated in the lab.

Nike InfinityRN 4 Midsole width in the forefoot
Test results
InfinityRN 4 118.4 mm
Average 113.7 mm
Compared to 297 running shoes
Number of shoes
100.5 mm
Midsole width in the forefoot
126.5 mm

Midsole width in the heel

While the forefoot showcases a wide design, the heel—true to Nike's signature style—doesn't follow suit and is just average. We've accurately measured it at 91.2 mm.

Nike InfinityRN 4 Midsole width in the heel
Test results
InfinityRN 4 91.2 mm
Average 90.5 mm
Compared to 297 running shoes
Number of shoes
74.9 mm
Midsole width in the heel
106.6 mm

Flexibility

Stiffness

At the beginning of our lab review, we discussed the dual purpose of the outsole cutouts: to reduce weight and enhance flexibility. Now, we're diving into the flexibility measurements. During our evaluations, it took just 15.8N of force to flex the shoe to a 90-degree position. 

This indicates that the InfinityRN 4 offers a flexible experience and doubles well as a walking shoe. However, it's essential to understand that this speaks to its longitudinal flexibility, not the torsional aspect.

Test results
InfinityRN 4 15.8N
Average 29.1N
We use an average of four tests. The video shows one of those tests.
Compared to 279 running shoes
Number of shoes
2.2N
Stiffness
94.4N

Difference in stiffness in cold

Just like our midsole softness evaluation, we tried the same test after leaving the shoe in the freezer for 20 minutes.

The outcome was disappointing. The shoe became much stiffer, and we had to exert 27.2N of force to bend it to the same point.

With a 71.6% increase, we're certain you'd feel the difference if you're in a cold-weather region.

Test results
InfinityRN 4 71.6%
Average 36.2%
Compared to 279 running shoes
Number of shoes
0%
Difference in stiffness in cold
148%

Size and fit

Internal length

Upon our initial try-on of the shoe, it felt really short to us. We immediately took precise measurements and found it to be 259.9 mm.

This is a noticeable 10.1 mm shorter than the 270 mm that Nike claims on their size charts. Most runners will likely need to go up at least half a size when considering the Infinity RN 4.

Nike InfinityRN 4 Internal length
Test results
InfinityRN 4 259.9 mm
Average 269.2 mm
Compared to 160 running shoes
Number of shoes
259.9 mm
Internal length
280.4 mm

Toebox width at the widest part

As a daily trainer designed towards comfort, we anticipated a generously spacious toebox—and we were delightfully satisfied.

Measuring at an impressive 99.9 mm at its widest point, it provides ample space and comfortably accommodates those with wide feet.

Nike InfinityRN 4 Toebox width at the widest part
Test results
InfinityRN 4 99.9 mm
Average 98.3 mm
Compared to 297 running shoes
Number of shoes
89.5 mm
Toebox width at the widest part
109.1 mm

Toebox width at the big toe

The excellence continues in the big toe area, where we found an impressive width of 80.0 mm.

This feature is a wonderful find for individuals with Roman or German foot shapes, as their pinky toe often struggles for space in narrower shoes.

Nike InfinityRN 4 Toebox width at the big toe
Test results
InfinityRN 4 80.0 mm
Average 78.2 mm
Compared to 171 running shoes
Number of shoes
60.4 mm
Toebox width at the big toe
92.5 mm

Tongue: gusset type

With its £170 price tag, we were curious to see if Nike had decided to improve their margins by using a non-gusseted tongue in the shoe. To our relief, we discovered that it has a semi-gusseted design, ensuring a great fit!

Nike InfinityRN 4 Tongue: gusset type
Test results
InfinityRN 4 Both sides (semi)

Comfort

Tongue padding

We measured the tongue's padding at 5.6 mm, finding it to be optimally cushioned. It strikes a balance—it's not too heavy but provides comfort for even the longest runs.

Nike InfinityRN 4 Tongue padding
Test results
InfinityRN 4 5.6 mm
Average 5.6 mm
Compared to 294 running shoes
Number of shoes
0.5 mm
Tongue padding
14.2 mm

Heel tab

Thankfully, Nike included a finger-loop heel tab! It's convenient and looks amazing.

Nike InfinityRN 4 Heel tab
Test results
InfinityRN 4 Finger loop

Removable insole

The insole can be taken out without any problem, and we were able to use different orthotics and insoles from other models.

Nike InfinityRN 4 Removable insole
Test results
InfinityRN 4 Yes

Misc

Reflective elements

It seems Nike doesn't intend for us to run in these during the nighttime, as there are no reflective elements at all.

Nike InfinityRN 4 Reflective elements
Test results
InfinityRN 4 No