Nike InfinityRN 4 Performance Review

The Nike InfinityRN 4 is in its fourth iteration. Some of the basics stayed the same from the Infinity Run 3, but the design and foam are drastically different. Nike is using the fourth Infinity Run model to introduce a brand new foam, ReactX.

ReactX “reduces the midsole’s carbon footprint by at least 43%…while simultaneously being more responsive, offering runners 13% more energy return.” In theory, that sounds great. Let’s get into how the Nike InfinityRN 4 performed during our extensive test period.

Sizing/Fit

Annie: I have to say, when I looked at the box and saw Nike had sent a women’s size 7, I was dubious.

I usually wear a women’s 6.5 in my running shoes and occasionally even go down to my “true” size 6 if a shoe runs on the roomy/long side. But I have never needed a size 7 in my life (unless you count the team shoe we wore for high school basketball that didn’t exist in anything below a 7, in which case I sucked it up and double-socked like a champ—which is more than I can say for my actual game, but that is neither here nor there).

Point being, this shoe runs short and snug, and Nike is aware of it enough to even recommend sizing up on their site. The 7 fits the way I’d normally expect of my usual 6.5, with a thumb’s width of space at the end and a comfortable toe box for my average-to-slightly-wide forefoot.

Seeing as I found myself in completely uncharted size territory, I imagine most runners are safe to go up a half size from the jump. Drew, how did you find the men’s pair? Was a half size up the way to go?

Drew: Unlike Annie, I first tried my normal size of the Nike InfinityRN 4. And it was basically the equivalent of applying a tourniquet to my foot. Cut off my circulation level of tightness. I usually want knit shoes to be tight because they mold to your foot over time, but this was a step too far.

Fast forward a couple of days to when I was able to snag a half size up and the fit was perfect. This has happened a few times over the years. A knit shoe can come off the production line small. My guess is that the machines that put the Flyknit together can sometimes pull the strands too tight. Whatever the reason, go a half size up and you’ll be in line with what you’d expect. My apologies to those large footers who have no half size options, you may be forced to skip this one.

Upper

Annie: The Flyknit was flexible but still had plenty of structure to avoid feeling loosey-goosey. Honestly, it’s beautiful and interesting to look at, and people are going to be happy to see this Flyknit as opposed to some of the less refined and sometimes downright plasticky versions that have been on other models in the Nike lineup as of late. It looks good, and more importantly, I always felt securely held onto the footbed.

That said, the Nike InfinityRN 4 is somewhat thick and was a smidge warm in hotter conditions. I also wasn’t crazy about how the topmost eyelets caused the lacing to cross over the tongue’s seam on top of my foot. It seemed like it was ripe to cause problems when lacing up, but I thankfully never experienced pronounced lace pressure or rubbing issues on the run. The tongue comes up kind of high, but my preferred running sock has both a heel tab and a little extra coverage at the front of the ankle, so I went unscathed. But word on the street is that you weren’t so lucky, Drew…Talk to us. Let us bear the burden of your suffering.

Drew: My Bombas socks also had a front tab meant to prevent this exact problem, but on a 10-mile run in the Nike InfinityRN 4, the admittedly older sock slid down a bit and the slightly pointy and rough tippy top of the tongue gave me a solid blister. This only happened on my right foot, but examining the tongue reveals that it’s the same on both shoes, a bit rough and pointy. It’s likely something you can avoid with proper sock placement but keep this in mind if you wear no show socks.

And while I did find the Nike InfinityRN 4 a little warm and a very effective sweat towel for my feet on hot, humid days, it’s exactly what I expected from a Flyknit shoe. The Nike InfinityRN 4 upper reminds me of the Free RN Flyknit from 2016, one of my favorite uppers ever. It’s soft, comfy, and molds closer to your foot the more you run in it.

Because the Flyknit upper is so good, I wish the tongue was more minimal and the heel a little less padded (like on the Asics Gel-Nimbus 25) so the whole shoe provided more of that minimal sock feel. But, that’s not really the purpose of the Infinity Run line, so I get why Nike made the decisions they did. Still, if you love the feel of raw, un-plasticked Flyknit on your feet, you will likely be very happy with the Nike InfinityRN 4.

Annie: Nike used a water-repellent liner in the toe that they describe as a measure to help keep your feet dry. But my greater concern was how the knit upper would fare when wet. I was afraid it might lose its structure and eventually stretch too much to remain supportive and keep my midfoot locked down.

After getting caught in rain that started as a mere sprinkle and escalated into a summer downpour, I’d say the liner was only effective when running on already wet pavement as opposed to when it was actively raining. Even under a light sprinkle, I could feel water soaking into the upper; and the moment conditions intensified, my feet were quickly drenched. That said, I was very impressed by how well the Flyknit kept both its structure and comfort even when utterly saturated with rain. But be forewarned if you are also a rain-or-shine runner: the upper was still wet well into the next day.

Did you get much in the way of water resistance, Drew?

Drew: The waterproof toe cap seemed more like flashy marketing than anything to me. The rain and humidity soaked the Nike InfinityRN 4 no matter what I did. And yes, they also took forever to dry. Taking out the insoles helped, as did leaving them in direct sunlight.

Wet summer weather is not the best environment for this shoe. In addition to the long drying period, my shoes now smell awful. With previous Flyknit uppers, I’ve taken out the insoles, thrown the shoes in a clothing bag, and run them through the washer with my workout clothes (cold or room temperature cycle). I’m going to have to do the same with the InfinityRN 4 to ensure some longevity for the upper.

Outsole

Annie: There’s no shortage of rubber on the outsole, which no doubt adds weight. But given that the Nike InfinityRN 4 is namely a workhorse daily trainer/cruiser built to last the miles, I see the extra rubber as a mostly good thing. I even felt comfortable taking the shoe on some dry stretches of packed dirt trails and fine gravel, though when things got steep (albeit by paltry midwestern standards), I did abandon ship and return to the paved path.

In the earliest moments of the aforementioned downpour, the outsole pattern felt a bit like walking around the parking lot with your cleats on after softball practice. But once I had a moment to adjust and the Nike InfinityRN 4 got good and soaked, the traction held its own on rain-covered, paved surfaces. I didn’t have much confidence when encountering anything metal in those conditions (like manhole covers, etc.), but there honestly aren’t many shoes that I’d fully trust to freely traipse upon such surfaces when wet or icy.

Drew, this outsole has a very different pattern from the three previous versions of the Infinity Run, right? Did you find it to be a good thing?

Drew: I found the new outsole pattern largely durable though I do see signs of wear. I’d expect the Nike InfinityRN 4 to get an average lifespan out of its outsole. As for the traction, I mostly felt secure.

Dry conditions weren’t a problem. The uneven pavement wasn’t an issue. However, random wet spots on wood and metal were the Nike InfinityRN 4’s kryptonite. Even uniformly wet pavement didn’t cause an issue, but the wood and metal caused slight slippage with every step thus taking away power from each foot strike. So let’s call the traction good but not great.

Midsole/Ride

Annie: I will leave it to Drew, Chris, and Jodi for the expert breakdown of what exactly puts the “X” in the new “ReactX” foam.

I only briefly ran in the original Infinity Run, but I remember the v1 React midsole as a little blocky when it came to its sculpting but still airy in its texture and ride. It had a comfortable dampening effect rather than anything particularly lively. I liked that midsole well enough, and if not for the pesky arch (which we’ll get to in a minute), I probably would have enjoyed many miles in the v1.

The ReactX here in the Nike InfinityRN 4 felt quite different—almost rubbery—and even kind of firm (especially for the first few runs). As a result, this new version still seemed sturdy and reliable but also a touch more capable of picking up the pace (though a speed shoe, this is not).

But I’m curious as to what Drew thinks, as he has far greater institutional memory when it comes to the Infinity line.

Drew: To me, ReactX is a slightly more bouncy version of React. It’s not as squishy as the OG React on the Epic React Flyknit, and as Annie pointed out, it can feel a little firm out of the box. It also feels a bit heavier…which is why several people I’ve talked to call the shoe bottom heavy.

But when you’re 6’6” and 200 pounds a shoe’s weight rarely registers. With the Nike InfinityRN 4, you’ll get the best rocker of the entire Infinity Run series (I’ve run in all of them). It’s just smooth and works well with the ReactX to provide a very consistent feel from heel or midfoot to toe. It’s not a pop off the toes like you’d get with a super shoe but instead, it’s more like the rocking motion you get with the Hoka Clifton 9 or the Saucony Endorphin Speed 3. It’s the type of motion that makes running feel like less effort and more like floating.

What did you think about the rocker Annie?

Annie: The rocker felt pronounced but mostly smooth (as opposed to falling off a cliff). I also found the geometry absolutely vital. With how dense the ReactX felt underfoot and the amount of rubber on the outsole, the shoe occasionally felt bottom heavy. The geometry helped soften the edges and gave the ride some needed finesse.

Speaking of edges, the shaping of the midsole—namely how built up the medial side foam is—did come into play for me, especially in combination with the next item on the docket: the arch…

The Arch(enemy)

Annie: I’m seeing if Drew will indulge me and lavishly give the arch it’s own heading because it was a rather defining feature of my experience in both the v1 and now in the Nike InfinityRN 4…and not in a good way, unfortunately.

Drew: If there’s one line of shoes on the market that merits an arch section, it’s the Infinity Run. The arches on the previous Infinity Runs have been one of the most polarizing features on any shoe in the last 4-5 years.

Annie: For reference, I have average, unremarkable arches. Yet while my left foot is accordingly easygoing and adaptable in most cases, my right foot sometimes decides she’s the straight-up Princess and the Pea. That lady has no chill when it comes to unwanted interference, and she has no qualms letting me know it.

I do think the arch is less harsh here than I remember in the original Infinity Run. I even placidly smiled at the support when briefly walking around in the Nike InfinityRN 4 before my first run in it. I was optimistic at that point. Once I got moving, however, the arch soon felt disruptive, and I even had some numbness in the forefoot and toes during my 5-mile maiden voyage.

The combo of the foam sculpting and the arch height pitched my feet laterally and caused me to lightly press into the shoe’s side walls despite having ample room in the toe box (again, in my half size up) and good midfoot lockdown. That led to some early discomfort on the outside edges of my feet where they were bearing more weight than usual.

Happily, the discomfort while running diminished significantly after breaking things in; but I mention it because even well into testing, I continued to feel the effects of being shifted out of my natural alignment after each run and ended up having to take some extra care with my recovery work as a result.

Drew, if memory serves, I don’t think you’ve previously had any problems with the arch in the Infinity line…Have you ever met an arch that was too high for you, or are you generally unbothered on that front?

Drew: I haven’t had problems with the arches in the Infinity Run, Infinity Run 2, or Infinity Run 3. That said, I could easily feel all those arches. And as someone with a high arch, that’s rare.

The arch on the Nike InfinityRN 4 is less pronounced, less noticeable, and less annoying. That said, it’s still there and a part of the shoe you’ll feel on occasion (just like Annie). If you’ve avoided the Infinity Run line due to the arch in the past, the InfinityRN 4 is also not for you.

I think Nike should make the next Infinity Run shoe in both archless and high-arch versions. I have a hunch that would take sales to a whole new level.

Nike InfinityRN 4 Summary

Annie: The Nike InfinityRN 4 has a lot going for it, and I think many, many people will find it to be a solid option to eat up a ton of miles. I’m sure its aesthetics will also make it a go-to for casual use—because that Flyknit…

I’m almost definitely in the minority, but in my case, the arch was the one downside that kept me from being able to fully enjoy the other good things this shoe has to offer. I was instead left with a mild case of déjà vu and some extra foam rolling to do. So, if you know yourself to be especially sensitive to extra arch support, I’d be wary.

If, however, you’ve worn and loved the Infinity in the past, have found you benefit from a higher arch in your shoes, and/or prefer a resilient ride that also provides a small insurance policy against overpronation, you’ll love how the Nike InfinityRN 4 cradles you as you cruise.

Okay, Drew. You’ve run in all four versions of this shoe now, and this appears to be the biggest update yet. What’s your verdict?

Drew: The Nike InfinityRN 4 is the best Infinity Run yet. As Annie mentioned, its casual appeal is going to be huge and a lot of people will use it as their theme park shoe, walking shoe, or chasing pets/kids around shoe.

On the running side, just like previous Infinity Runs, the arch will likely be the deciding factor in whether you like it. Since it’s less pronounced, some people will finally be able to enjoy an Infinity Run, but most of those burned by previous arch pains should still stay away.

The rest of us will get a very, very good daily training shoe that’s ready for lots of highly comfortable miles.