Material Matters: How Super Is Too Super for Running Shoes?

The super shoe phenomenon went into overdrive in 2017 when elite Kenyan runner Eliud Kipchoge attempted to break the two-hour marathon barrier with the aid of Nike’s first super racer, the Vaporfly Elite. He didn't reach his goal at this event, but it did send brands racing to create the fastest shoes possible. Using the latest foam technologies and springy carbon fibre plates, everyone was looking to provide unparalleled cushioning and energy return.

In the seven years since, there's been a slew of innovation that has taken models past the point of super and into the ‘too super’ category, with many of them being banned from competitions thanks to new restrictions by World Athletics – the international governing organisation that regulates track and field sports. The new rules came after Kipchoge’s second and successful attempt at breaking the two-hour marathon hurdle in 2019, where he wore an even more advanced Nike shoe: a prototype of the Alphafly Next%.

While the new rule book helped even the playing field, the criticism that super shoes enhance performance beyond the body’s natural ability still generates headlines. The fact is that super shoes do help runners achieve faster times. It’s not just a coincidence that since their introduction in 2017, records for nearly all endurance running events from the 5000 metres to the marathon have been broken. It’s been a debate in running culture if this advanced footwear is a form of cheating or just part of the evolution of the sport due to other technological advancements in footwear, apparel, equipment and health science throughout time.

To understand the controversy better, let’s get up to speed on the super shoe phenomenon, analyse how they make runners faster, and why some have been outlawed because of their souped-up tech.

What a Super Shoe Is and How It Makes You Run Faster

There is no specific definition for what can be categorised as a ‘super shoe’, but in general, a running shoe is considered ‘super’ if it has the following three characteristics: a thick midsole with advanced foam, rigid plates usually made from carbon fibre and an ultra lightweight design.

Thick Midsole with Advanced Foam
Super shoes have thicker midsoles than standard running shoes and this thickness, particularly at the heel, supplies more cushioning for less fatigue on the runner’s foot. The thicker sole also adds extra length to the runner’s leg, which is theorised to increase their stride and help them run further, faster. The midsoles of most super shoes are around 40mm thick, which is the maximum height allowed by World Athletics for competition.

All athletic footwear brands have their own proprietary foam formulas composed of three main foam types: PEBA (polyether block amide), EVA (ethylene-vinyl acetate) and TPU (thermoplastic polyurethane). PEBA – also known as Pebax if it’s manufactured by the brand that invented it – is the newest and most advanced foam on the market and it’s found in most running shoes considered ‘super’. Because of its advanced composition consisting of two polymers – polyether, a soft, flexible and elastic material, and polyamide, a rigid, durable and strong material – it offers the best of both worlds. It’s lighter and more energy-returning than traditional EVA and TPU foam soles yet still stable and durable enough to support a runner’s feet over long distances. When adidas BOOST debuted in 2013, people everywhere were amazed by the TPU foam's bouncy feel; however, while BOOST is still a great cushioning platform, it pales in comparison to PEBA. BOOST was found to deliver 75.9 per cent energy return, while Nike’s ZoomX PEBA foam provided an impressive 87 per cent return in energy.

Nike’s ZoomX led the charge for PEBA foams, but most brands now have their own PEBA formulas for their super shoes, including the Saucony PWRRUN PB, ASICS FF TURBO PLUS, PUMA NITRO Elite, On Helion HF, and New Balance FuelCell. Each of these foams varies slightly in factors like energy return, stability and durability, and it’s really just up to the consumer to test each out and find what works best for them.

World Athletics has no rules regarding what the foam in a competition shoe can be made from, just how thick it is. The organisation hasn’t publicly stated why they landed on 40mm for the maximum height allowed, but it is speculated that the limit is to prevent brands from housing too many shank plates or other future technologies in the midsole.

Rigid Plates
Super shoes also include at least one rigid plate, usually made from carbon fibre or carbon-infused materials. These thin, lightweight and flexible yet sturdy plates are housed inside the midsole, providing structure and stability underfoot. The scoop shape of many of these shank plates combines with the thick sole to create a rocker or teeter-totter effect that increases energy return and a sense of forward motion. Think of the plate as a tool that helps the foam compress and expand more quickly to propel you forward with less effort from your body. Typically, the shoes make the wearer feel more like they’re running downhill rather than on a flat surface, which significantly reduces physical fatigue, especially over longer distances.

World Athletics regulations state that a competition running shoe may contain only one rigid plate, as more than one makes the shoe unfairly springy. This ruling goes back to the Alphafly Next% prototype that Kipchoge wore for his astounding 1:59:40 marathon finish at the INEOS 1:59 Challenge, which no doubt prompted the new regulations announced in early 2020. The most super of all super shoes at the time, the speedy prototype featured not one, not two, but three carbon fibre plates housed in the midsole, which worked with the thick ZoomX foam to catapult Kipchoge forward with each stride.

Ultra-Light Weight
If a runner has less weight on their feet, they experience less fatigue and in theory, can run faster. Brands have gone to great lengths to reduce the weight of the uppers to coincide with the lighter PEBA soles, and it’s now possible to do so without sacrificing durability. World Athletics can’t regulate how light a shoe is, so the only challenge brands have in this respect is how to balance weight reduction with durability. If the materials are too flimsy, the shoe won’t be in one piece by the time you cross the finish line.

And yet, there has still been controversy surrounding the lightest racer on the market. In 2023, adidas released the Adizero Adios Pro Evo 1, featuring a see-through upper, non-compression (less dense) foam sole, and extra-thin rubber outsole that only covers the forefoot. This all combines to create a construction that is so delicate adidas recommend wearing each pair for only one race. The 4.8-ounce, $500 featherweight was deemed ‘wasteful’ by some environmentally-conscious critics, including a group called the Green Runners who publicly asked adidas to cease production of the shoe.

Nonetheless, it still delivered serious results. In 2023, Ethiopian runner Tigst Assefa wore a pair while setting a new women’s marathon world record of 2:11:53 at the Berlin Marathon, obliterating the previous record by more than two minutes. At 4.8 ounces, the Adizero Adios Pro Evo 1 is significantly lighter than other super racers on the market that typically weigh in at 7 to 8 ounces, like the Nike Alphafly 3 at 7 ounces or the Saucony Endorphin Elite at 7.2 ounces.

The New ‘Illegal’ Training Shoe Category

After World Athletics set new regulations, brands adjusted their super shoe designs, but only for dedicated racing models to make sure elite athletes can still legally compete in their shoes. But brands are now also producing what are called ‘super trainers’ – running shoes for daily training that defy the midsole height and carbon fibre plate restrictions. Many casual runners love the look and feel of these pillow monsters, as the thick bottoms absorb shock and help dampen impacts that other running shoes can’t. Super trainers won’t make you the next Eliud Kipchoge, but if you’re logging serious miles, they should theoretically increase your range and reduce wear and tear on the body. Examples of ‘illegal’ super trainers include the Saucony Kinvara Pro at 42mm, the ASICS Superblast 2 at 45mm, and the adidas Adizero Prime X 2.0 Strung at 50mm with two carbon-infused plates.

To date, the most extreme super trainer to hit the market is the PUMA Fast RB NITRO Elite, which rises to an unprecedented 58mm on the heel and includes three pieces of PUMA’s PWRPLATE carbon fibre. Released in a run of only 1000 pairs in late August 2024 for $350 USD, the Fast RB NITRO Elite (RB stands for ‘rule breaker’) is being called the ‘world’s most illegal running shoe’, and its radical design – the heel doesn’t touch when the shoe is sitting on a flat surface – makes it look more like a concept sneaker that’s out to grab attention than a serious performance model. In their YouTube review, The Run Testers describe it as ‘a fun shoe, just not necessarily a very practical one’. But the fact remains that these slingshots for your feet do indeed exist, and at least a select amount of people will be running in them.

Whether soles will get even thicker is yet to be seen; however, in the long run, the thickness will almost certainly decrease as technology advances. ‘It isn't about the stack height as much as the foam technology,’ says Thomas Neuberger, founder of Believe in the Run. ‘We have to stack the foam to get the desired energy return and comfort. If technology changes and we can get thinner layers of foam to produce high energy return and comfort, the stack heights will come down.’

Super Shoes: Only the Beginning or a Passing Fad?

Trends come and go in the running world. It wasn’t that long ago that runners everywhere donned the Nike Free franchise and Vibram FiveFingers to stay as close to the ground as possible. The complete opposite of super shoes, these minimalist platforms were designed to mimic the experience of running barefoot to reportedly strengthen feet, prevent injuries and improve balance.

Super trainers may be the trend popping off right now, but they are absolutely here to stay. And that’s a good thing, as more options make running better and more enjoyable for all runners. Testing the boundaries of innovative footwear design will continue as long as there’s money to be made. ‘The brands are playing and pushing the limits to see what happens when you bend the rules. They probably already have prototypes with higher stacks, but releasing them will depend on consumer demand,’ says Neuberger.

What is now a controversial phenomenon will eventually become just another category in the running shoe market, and unless you’re a professional athlete watched by World Athletics, super shoes can be as super as you want them to be.