In a sport where preventing chafing can be the difference between PR and DNF, the new generation of running shoes with knitted uppers might be the holy grail.

By Jordan Rapp

Before we get into a discussion of knitted uppers, we first need to talk a bit about the difference between knitting and weaving. Especially when all the production is being done by machine, the difference is somewhat nuanced. When we talk about knitted uppers, we are not talking about a little old lady with knitting needles making your shoe: these are all highly engineered fabrics. But although the “how” of knitting is interesting, this is about the possibilities that knitting opens up. Why make knitted uppers?

Knitting is basically how you make a sock. Knitting is the process of interlocking loops of thread, allowing you to form an object that closes without seams. Fundamentally, knitting allows you to make a “shape.” Weaving, on the other hand, is what you use to make a sheet of fabric—by crossing threads at right angles to each other, which you then cut, sew, or otherwise bond into a shape. You can make a sock out of a woven material, but you need to have a seam where it closes. And, at least in certain applications, seams are bad.

While Nike was clearly first to market by a few months, both companies had spent years working on the process of knitted uppers.

Now these are clearly not the only two way to make fabrics. Common materials, like leather or synthetic leathers have an entirely different structure. What is most critical is that, traditionally, running shoe uppers were made by stitching (and/or bonding and gluing) together patches of material until you got something that held your foot in place. Knitted uppers, by contrast, allow you to have a one-piece upper: no seams; no panels, no stitching. In some cases, you may still overlay other materials to add support in certain areas, but where your foot goes, you can have a shoe that fits more like a sock. As to why this is a good thing—well, there’s a reason why you wear a sock inside your shoe.

The company that is currently most aggressively pursuing this approach to making knitted shoes is Nike. Some of this is the result of a court battle Nike won over Adidas in late 2012, when a judge in Germany ruled that Nike’s Flyknit technology for creating knitted uppers was protected by a patent and that Adidas could not make shoes with their Primeknit technology. This was a huge win for Nike. While Nike was clearly first to market by a few months, both companies had spent years working on the process of knitted uppers. A later ruling overturned the initial Nike victory, and Adidas is once again making Primeknit shoes, but knit technology has lost momentum at Adidas, and it certainly is not part of the mainstream the way it is at Nike.

Ironically, my first experience with knitted uppers comes from a pair of Adidas Primeknit Racers, the limited edition running shoes made for the 2012 Olympics. (I have pair 393 of 2012 pairs. I hesitated to run in them because they are truly a collectors’ item—new-with-tags pairs go for $500 on eBay.) This shoe later became a standard-issue shoe, and this was the shoe that Nike and Adidas fought over in court.

Since Nike’s court victory was overturned, this technology has started to trickle down to smaller brands because it was clear that Nike was going to have trouble enforcing a patent. One of the key points in Adidas’s rebuttal was that knitted materials in shoes has been in use since the 1940s and was hardly novel. The court agreed, both in Germany and the U.S., though the two brands are still duking it out in front of the U.S. Patent Office. Based on absolutely no legal expertise, I don’t see Nike winning this fight in court—but it doesn’t really matter. Nike Flyknit shoes are dominating where it really matters: sales. Flyknit is huge and Primeknit barely registers. But beyond the battle between these two titans of industry, the technology is out there in the factories, and more brands are taking advantage. For example, Newton makes about half their line—their POP2 and POP3 models, which are geared more towards casual runners—using knitted materials in the upper.

To give me some insight into this technology, I was fortunate to have the expertise of Kate Libonati, one of Nike’s tech reps, and Dave Jewell, who worked at Adidas in running shoe development before he worked at Zoot. Both gave me some insights into the critical question of “why?” Why do running shoe companies want to make shoes in this way?

Libonati gave me some of the history on the Nike side. As with a lot of Nike’s inspirations, this came from legendary Oregon track coach Bill Bowerman (he of the waffle-iron soles). Bowerman wanted shoes to fit more like socks. In 1985, Nike introduced the Sock Racer, a shoe that had quite a following among triathletes of the day. In typical fashion, triathletes were ahead of the curve. The Sock Racer lacked the overall functionality of current Flyknit shoes, but it set an ideal out there that Nike engineers worked for decades to achieve.

According to Jewell, the real investigation into using knitted uppers began in the middle part of the 2000s with the idea of “no sew” construction. How could shoe companies make a shoe without stitching or bonding? Less stitching meant less overlay, making shoes lighter. It also meant you had fewer potential places where rubbing would occur (more problematic with stitching than with bonding, but any overlay is a potential hotspot). And, ideally, less labor cost in terms of sewers. The cost savings aspect has not yet been realized. Nike says it’s more technically challenging to create a Flyknit upper, and these shoes still carry a significant price premium over the equivalent mesh-upper shoe. But Jewell believes the cost aspect will be a significant driver towards adoption. As with anything, in the beginning change comes with a cost.

The evolution from “no sew” construction to knitted uppers followed from the ideal of a one-piece upper. A one-piece upper would have truly no sewing of any kind, and knitting was the way to achieve this. According to Jewell:

“Not long after [no sew] the questions of ‘what if’ began to come. It came from brand people either in product creation or in the advanced concept groups. What if we could create a one-piece upper? What if we could create an upper with no overlays and no stitching at all? The Advanced concept groups either briefed their sources or their sources came to them with a new manufacturing. It’s not 100 percent clear who did what first, but the end result was clear:

  1. Through a computer, they can knit to any specification.
  2. They can put a tight weave where there once was an overlay with the same performance.
  3. They can create stretch in the vamp [forefoot area of the shoe] that creates a more custom fit for the runner.
  4. They can test new uppers faster than ever before.
  5. There is a high setup cost for computer stitching.
  6. There is great savings in labor, and with a fully knitted upper there is no upper-cutting die needed (big cost savings).

The challenges were significant, though. According to Libonati, at first, Nike introduced Flyknit with the idea of it being a “podium” shoe rather than a shoe designed to actually function. It was more a showpiece of Nike’s technical prowess than anything else. The apparent simplicity of a one-piece upper belies its technical complexity. Instead of mixing different panels, all the different materials need to be mixed in the knit. Flyknit is a blend of polyester, nylon and spandex. Each “recipe” differs depending on the shoe type. The ultraform-fitting “natural” Nike Free 3.0 has a very elastic and very snug fit. The speed-oriented Flyknit Racer has a more structured upper that isn’t quite so snug on the foot.

In all cases, though, the fit of a knitted upper is a change, and it can be an odd one. According to Jewell, the different feel of the shoes is a huge obstacle on the sales side. People have certain expectations about how tight a shoe can be. I noticed this myself when I first ran in my Adidas Primeknit shoes. At first I laced them about as tightly as I would lace a regular shoe. But as a result, the shoe ended up being pretty sloppy on my foot, and after a long run I had quite a few hot spots on the soles of my feet from moving in the shoe. After a few trials, I have found that if I lace these shoes very tightly they fit great. The upper moves a lot with your foot, but not in a bad way. If I laced a regular shoe that way, it would be far too tight once I got into my run. Nike’s goal is to have a shoe that, according to Libonati, “hugs the foot,” but runners tend be wary of that. I’ve run in shoes that have “hugged my foot” before, and I typically lost a lot of toenails after I did. But I don’t have the same sense that would happen in a knit shoe.

The shoes will get wet, but they don’t retain any more water than a comparable upper made of more traditional materials.

Of course, not all knit shoes are created equal or in the same vein. Newton seems to be using knit construction more to eliminate seams than anything else. Overall, the shoes still have roomy toe boxes and don’t have the “hug the foot” quality of the Adidas or Nike shoes, but they do offer a very nice feel that’s distinct. Newton seems to be introducing knit construction more slowly, perhaps not surprising for a brand that has far fewer models than Nike or Adidas and that is already is taking a risk on the technology side.

But even at Nike, the ideas behind knitted uppers are influencing construction of shoes across the line. Nike has only three Flyknit shoes on the running side (they also make basketball and soccer shoes using knit construction, as does Adidas), but they have six shoes that use what they call Flymesh, which is really an engineered mesh (woven) upper that takes design cues from the knitted shoes. The most notable example of this, to me, is the hugely popular Lunaracer+ 3, which you’d never guess has a mesh upper unless you read the spec sheet. It looks like a knitted shoe, but it’s not. And other staple shoes in the Nike lineup also have knitted qualities. When even the Pegasus—the flagship Nike running shoe—has knit tech in its upper, you know that’s big. Libonati emphasized that Flyknit and Flymesh are not just gimmickry or niche shoes. I don’t know that it’s ever going to be a total transition, but I do think that this is going to be the “process” behind how Nike (and Adidas and most other companies) make more of their shoes. I haven’t spent enough time in the shoes to declare that knit technology provides a better overall experience, but I do understand the problems that it is trying to address and feel confident that it is better as a design ideal. And of course it is one that will continue to evolve.

One challenge that the engineers couldn’t address—and this is really the job of Nike’s fleet of technical reps like Libonati—is how people perceive the new shoes. The big fear is that, like a knitted sweater, a knitted upper will unravel if it snags. Libonati assured me that they would not. So you don’t have to worry about your shoes unwinding around your feet as you run down the road. Another common perception is that they will hold more water. Again, I think people think of more traditional knitted garments when they come up with these ideas. The knit upper isn’t particularly hydrophobic—it’s not like the totally unique Tyvek upper of the Nike Mayfly or the flexible, plasticky upper of the original Lunaracer, neither of which seemed to retain any water at all. But Libonati said that again, looks are deceiving. The shoes will get wet, but they don’t retain any more water than a comparable upper made of more traditional materials. According to Libonati, there really are no drawbacks to the end user, other than price, and if Jewell is right, that too may cease to be an issue.

Shoes are really too unique to ever yield to a one-size-fits-all approach. This is part of why so many brands making so many different shoes continue to thrive. But especially in a sport where sockless wear and aversion to seams and chafing are paramount, I’m excited to see knitted uppers continue to evolve and improve. For certain applications, I don’t think socks will ever go away. But with the particular demands of tired legs, swollen feet, bad mechanics and the ever-present need to douse yourself at aid stations, triathletes’ feet could use all the extra help they can get. An absence of seams sounds pretty good to this Ironman racer, and I’m wondering if it might sound even better with 6 miles to go on race day.


august-2015-coverThis first appeared in the August 2015 issue of LAVA. Get your issue here.

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