What’s it going to take for the first person to run a marathon in less than two hours? Athletic apparel giant Nike is betting that, in addition to optimally trained athletes and ideal conditions, it will require finely tuned footwear with innovative new technologies unlike anything we’ve seen to date.

Today, Nike unboxed a trio of shoes coming directly from research for its Breaking2 project, the company’s effort to train and equip three of the world’s top distance runners—Eliud Kipchoge of Kenya, Lelisa Desisa of Ethiopia, and Zersenay Tadese of Eritrea—to break the barrier.

Each will wear his own customized version of a new racing shoe, the Zoom Vaporfly Elite, in their attempts at the mark. The technology used in those exclusive pairs will trickle down to customers in the form of the other two shoes—the Zoom Vaporfly 4% and the Zoom Fly. (Both are expected to be available June 8.)

All three shoes have an emphasis on reducing weight, maximizing aerodynamics, delivering extremely soft cushioning, and offering a responsive toe-off suited for running fast. They'll do that with innovative new lightweight foams and with plates. The Vaporfly Elite and Vaporfly 4% each get a carbon-fiber plate; the Zoom Fly's plate is made of a less stiff carbon-fiber nylon.

Here’s a look at what goes into each shoe.

ZOOM VAPORFLY ELITE

A new, light foam allows the Vaporfly Elite to have thick cushioning underfoot without adding extra weight. Jeff Dengate

Unless your name is Kipchoge, Desisa, or Tadese, forget about getting your feet in a pair of the Vaporfly Elite. Those shoes are Frankenstein-looking prototypes being built only for the sub-two effort. Each features totally unconventional sculpting and radical design, and is built to the individual runner’s preferences, fit, and biomechanics.

A key to the shoe’s performance is a new lightweight foam called ZoomX. In the past, you could choose either soft cushioning or responsiveness. The Vaporfly Elite has a thick slab of lightweight cushioning to help protect the runners’ legs from the pounding of 26.2 miles on pavement, but it’s still resilient on push-off.

Rather than standard conventional midsole materials, the foam is made from Pebax, according to Nike. The company won’t go into details about the material, but Geng Luo, senior researcher at the Nike Sport Research Lab, tells us the “magic is in the processing of the foam to deliver this performance.” Previously we’ve seen Pebax used in running shoes more for plastic bridges and other molded parts. For example, Mizuno has used it in a Wave plate, and The North Face uses it for cradles to hold the heel in place. Pebax has a lower density than some thermoplastic alternatives (thus, it’s lighter), but is also flexible, resists impact, and returns energy.

Nike says this new foam weighs roughly one-third as much as Cushlon—the midsole material you’ll find in the Pegasus—yet delivers more cushioning than that shoe. It also delivers 13 percent more energy return—Nike reports ZoomX returns 85 percent. What that means is the shoe will feel bouncier and reduce the energy lost with each foot strike. In tests of running-shoe cushioning systems at the Runner’s World Shoe Lab, we typically see “energy return” (the percentage of energy input that is recovered; the rest is generally lost as heat) in the 40 to 60 percent range, with Adidas’s Boost topping the charts near 70 percent. Our measurements come from an impact test of a full sole unit, which includes rubber outsoles and layers of glue. This is also how Nike has said it tested ZoomX to arrive at its 85 percent energy return measurement.

Because of the foam’s light weight, Nike is able to use more of it, too. The stack heights (a measure of all materials that separate your foot from the road) for the Vaporfly Elite are expected to be 31 millimeters in the heel and 21mm in the forefoot. That’s very thick for a racing shoe. For comparison, the Zoom Structure 20, a soft, stable, everyday trainer, is just 2mm thicker in both locations. Yet the Vaporfly Elite is expected to weigh somewhere around 6.5 ounces—the shoe is still being tweaked so an exact figure isn’t available. (For comparison, the Structure weighs 10.7 ounces.)

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Sandwiched between two layers of the foam is an extremely stiff carbon-fiber plate that runs the length of the shoe. The forefoot of the plate is curved, while the midfoot and heel slant upward and taper—imagine the footbed in a woman’s high heel shoe, to get an idea of its shape. That sweeping configuration is designed to increase stiffness much like a track spike does, directing power over the big toe to reduce energy loss at push-off. The curvature at the forefoot is to reduce any undue workload on the calf, which would cause fatigue over long distances.

The unusual, tapered heel of the Vaporfly Elite is intended to reduce drag.

The plate is invisible in the finished product, but the shoe’s novel heel most certainly catches attention. The midsole tapers to an exaggerated point in the back to reduce drag, meaning the runner uses less energy to slice through the air. The benefit may seem quirky and prove small, but it may be tangible when you’re counting every second over such a long distance.

Another eye-catching feature of this shoe is its slipper-like shape. The entire shoe is extremely narrow through the heel and waist, but it bulges into a wide base under the ball of the foot—necessary to add stability at the late stage of the runners’ strides, given the shoe’s tall stack height and narrow build.

The upper is also tailored to each athlete, with a Flyknit stitched like a second skin for that runner’s foot. The yarn is knit with monofilament along the lower half of the shoe to reduce stretch and add structure, without adding any overlays or weight. The prototype we saw has a high-cut collar, but each athlete will be able to give input about things like collar height to suit his preferences in the coming weeks.

The outsole is still in the works, too, said Bret Schoolmeester, innovation director at Nike who briefed us on the shoe last week in New York City. It’s being designed specifically to suit the exact surface and conditions of the Formula One race track in Monza, Italy, where the athletes will make their sub-two attempt. The prototype we saw had a very thin layer of black rubber covering most of the forefoot (though foam was exposed in the sculpted areas near the toes) with two smaller patches of white rubber under the heel. Durability isn’t a concern, because the shoe has to last only this one race, delivering enough traction to minimize energy loss.

RELATED: Hear more about Nike’s Breaking2 attempt on this week’s Runner’s World Show podcast (new episodes each Thursday). Subscribe here.

The Vaporfly Elite is a custom shoe designed for the Breaking2 project and will not be commercially available.

ZOOM VAPORFLY 4% ($250)

For highly competitive runners, the Zoom Vaporfly 4% delivers the same high-performance technology as in the Vaporfly Elite, but with an off-the-shelf fit. The shoe's name is a nod to the improvement in running economy a runner can expect from wearing the shoe compared with other racing shoes like the Zoom Streak 6 racing flat. Basically, a runner wearing the Vaporfly 4% would be able to maintain any given pace while using 4 percent less energy. Nike reports that in lab testing done by Rodger Kram at the University of Colorado, oxygen consumption and CO 2 expiration were measured to determine how much energy a runner used to maintain a set pace. On average, runners consumed 4 percent less energy. Nike expects an even greater benefit by fine-tuning the Vaporfly Elite models to each of the runners chasing the two-hour mark. In both cases, if you're expending less energy, you'll be able to run faster.

As with the Vaporfly Elite, that efficiency gain is in large part due to the new ZoomX foam. The thick foam looks more Hoka-esque than like a racing flat. And in fact, the material delivers cushioning on par with beefier trainers. And it still offers a reported 85 percent energy return, like the Vaporfly Elite, according to Nike. We currently have the Vaporfly 4% in the RW Shoe Lab, but testing is not complete to confirm that figure. If it delivers 85 percent, it would be truly industry-leading.

The Zoom Vaporfly 4% has the same features found in the shoe for the three elite runners—minus the precise personalization. Nathaniel Welch

Like the Vaporfly Elite, the Vaporfly 4% has tall stack heights. The heel height is expected to be 31mm tall and the forefoot 21mm. The shoe also gets a stiff carbon-fiber plate that runs the length of the shoe. One difference between this plate and the one in the Elite is that all 4% plates will be tuned to the same stiffness—the runners trying to break two hours have input on how stiff they want their carbon-fiber plate.

The midsole of the Vaporfly 4% also tapers to a point in the back to reduce drag, though less dramatically than on the Elite version.

The shoe’s upper is a thin layer of engineered mesh to help keep weight in check while still firmly locking the foot in place. It also offers a lot of ventilation, especially in the toebox. There’s no heel counter (the plastic cup that wraps around the back of the foot) in this model, since it’s suited for efficient runners on race day. Instead, it uses a couple of thinly padded patches and sueded reinforcements to secure the heel inside the flexible upper. These weight saving measures let this shoe check in at just 6.5 ounces for a men's size 10, on par with the Elite version.

Early prototypes of the Vaporfly 4% have already had strong showings on some of running’s biggest stages: Galen Rupp, Amy Cragg, and Shalane Flanagan all wore them during last year’s Olympic Marathon Trials. The prototypes captured the first three places in the men’s marathon at the Rio 2016 games, and Kenenisa Bekele wore a pair when he ran 2:03:03 at the 2016 Berlin Marathon—the second fastest marathon ever.

Messaging on the heel of the Vaporfly 4% refers to the improvement in running economy Nike says the shoe provides. Jeff Dengate

ZOOM FLY ($150)

For the rest of us who wouldn’t usually wear a racing flat for 26.2 miles but still want to run fast, the Zoom Fly boasts the same construction philosophy yet is engineered for better durability. First, the foam is different—it uses a soft Lunarlon carrier with a new core foam on the inside. While this new material weighs more than the Zoom X, it’s still lighter than Cushlon and will be softer than the current Pegasus.

The Fly also has a propulsion plate running the full length of the shoe, but it’s made of a carbon-infused nylon that’s not quite as stiff as what’s found on the 4% and Elite versions. The geometry remains the same, however, to deliver a springy toe-off at racing speeds.

The Zoom Fly is designed to be more durable than the other Nike models. Jonathon Kambouris

The outsole is more substantial, too. It uses a foamed rubber for lightweight traction. We saw a similar compound on the most recent Vomero 12. It’s an incredibly compliant and quiet material that is smooth underfoot and doesn’t show wear easily.

RELATED: Find the best pair for you with our New and Improved Shoe Finder Tool

While heavier than the 4%, the Zoom Fly is expected to weigh just 8.5 ounces for a men’s size 10. It will feature stack heights of 33mm (heel) and 23mm (forefoot), and the Flymesh upper will be slightly more standard construction, including a lightweight heel counter and midfoot Flywire cables for a more secure fit.

At 8.5 ounces, the Zoom Fly is heavier than the other new Nike shoes while still being a lightweight pair for runners. Nike

WILL IT WORK?

It remains to be seen whether the Vaporfly Elite will deliver the first sub-two hour marathon. And we’re eager to see how the new Vaporfly 4% and Zoom Fly perform on the feet of age-groupers and recreational marathoners.

We just got pairs of the latter two into the RW Shoe Lab, and they’re undergoing a battery of tests. We’ll be taking a look at muscle activation of runners wearing the shoe and running at 5:30 per mile pace. Plus we’ll be doing our standard battery of mechanical testing—measuring cushioning, flexibility, heights, and weights. Stay tuned for more results soon.

Jeff Dengate Runner-in-Chief Jeff is Runner-in-Chief for Runner's World, guiding the brand's shoes and gear coverage.

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