Foam, A Friend
Why the new generation of foam midsoles is a boost to your running
Soft and bouncy midsoles are the hottest feature in shoes right now. Here’s what that means for your running
Sound familiar? No doubt. Last September, Brooks revealed its DNA AMP foam, also touting a blend of cushioning and energy return. In 2017, we saw Altra design its first shoes with the cleverly named Altra Ego foam, which – you guessed it – distinguishes itself by its soft step-in feel and bouncy ride. There’s also Under Armour’s new HOVR foam, Reebok Floatride Foam, Saucony Everun and New Balance Fresh Foam. It seems that every major shoe company now makes its own hero foam. But the question is: does it really make for a better run?
How we got here
To understand what made the world ready for bouncy-foam shoes, let’s rewind a few years.
In 2009, Christopher Mcdougall wrote a book called Born to Run, which challenged what was historically accepted about running shoes – namely, that perhaps we didn’t need so much shoe – and some believe it launched the barefoot or minimalist movement. Propelled by plenty of new research touting the benefits of light, barefoot-like shoes, minimalism experienced a meteoric rise. But in 2012, a class-action lawsuit against Vibram Fivefingers for deceptive advertising was the loud thud that marked the end of the minimalist running movement. At that point, many runners sidelined with injuries found minimalist shoes to be untenable, and most of the running community quickly returned to shoes that offered more padding.
But by that point, the world had changed. The research that led the minimalist movement, proving that shoes didn’t work to prevent injury as we had once believed, didn’t just disappear. Throwing out running shoes altogether wasn’t the answer, but neither was turning back to overbuilt, stiff, heavy, controlling shoes. One researcher, Benno Nigg, professor emeritus of kinesiology and director of the Human Performance Lab at the University of Calgary, Canada, suggested that your body knows best. His studies revealed that running shoes chosen simply by which felt the most comfortable were also the most efficient and best at reducing injury. Common runner knowledge shifted and comfort usurped control as the basis for shoe selection. With running-shoe companies no longer able to successfully market their multi-density soles with plastic posts, shanks and trusses, the properties of the foam itself rose in importance – and runners were ready to pay attention.
The energy surge
Enter the Adidas Boost. You can trace the running industry’s foam obsession back to a compound in this shoe, introduced in 2013. While running shoes have used foam for cushioning since Forrest Gump’s 1972 Nike Cortez, Adidas’s Boost foam promised something new: energy return.
The term, while great for marketing, can be a bit deceptive. Let’s be clear, no shoe will defy the second law of thermodynamics and actually create energy that will do the running for you. The energy for your stride comes from you pushing against the ground. ‘ When you put something soft underfoot, it’s robbing energy,’ says Golden Harper, founder of Altra. ‘The best foam in the world will never return energy.’
Martyn Shorten, a biomechanics expert and director of the RW Shoe Lab, can quantify that energy loss. Most shoes with traditional foam (called EVA) tend to dissipate 40-60 per cent of the force needed to compress them. The best new foams lose only
around 30 per cent of the energy. Though ‘energyreturn foam’ is a bit of a misnomer, we admit it is sexier than ‘less-energylost foam’, so we’ll stick with it. And, while not as amazing as gaining energy, losing less energy is a good thing.
And consumers agreed. Sales of Boost shoes fuelled double-digit growth in running revenue for Adidas in the ensuing years, and the Boost foam rejuvenated the once-slumping brand among retailers and runners – so much so that Adidas has struggled to keep up with demand.
Hooked on a feeling
Put aside physics and what the new foams can’t do, and what really matters is how the material interacts with your stride. New foams deliver two properties that had been mutually exclusive: cushioning and responsiveness. Before Boost, shoes felt soft or fast, but never both.
Energy-return foams accomplish both with a well-timed reaction. The cushioning dissipates excess forces, but unlike old marshmallowy foams, energy-return soles then firm up underfoot, which allows you to push off powerfully. ‘It’s not about absorbing energy,’ says Spencer White, vice president of Saucony’s Human Performance & Innovation Lab. ‘We want to take that force you create in landing and help you generate force so you can move.’ It’s the difference between bouncing on a soft pillow and on a trampoline.
In the end, as Nigg’s research shows, it comes down to what you feel. And what you feel is probably something new and amazing. ‘[Foam] feels soft and comfy when standing, and firmer and faster when moving quickly,’ says Harper. Perhaps more revealing than the physical feel is the emotional response. ‘ We’ve heard a lot of “It makes running feel fun!”’ says Kim. ‘It’s not something we usually hear.’
To foam or not to foam?
As magical as new foams may feel, they aren’t for everyone. ‘Shoes are so personal,’ says Harper. ‘There will be people who put on an Ego shoe, and it doesn’t connect with their stride, doesn’t feel good underfoot.’
This has always been the case with shoes, but new foams can be even more finicky because of the timing of the bounce-back. ‘The response is focused to a narrower range of runners,’ says Shorten. Which is why there will never be a holy grail of foam for all. ‘In the past, we searched for the one perfect shoe,’ says Kim. ‘ What we’re realising now is that doesn’t exist. There are distinct populations in the huge world of runners. The idea that you can make one shoe that can work for all the runners in the world seems just a little bit crazy.‘
Instead of making one ideal, brands are finetuning foams to maximise different experiences and letting runners decide what they like best. The feel of each foam differs depending on each runner’s unique weight, stride, speed and mileage, which also means you might prefer a different foam on different days. Kim says Eliud Kipchoge – he of the 2:00:25 marathon – likes the new Epic React, but only for easy runs. You may find one foam feels best for your fast days but that you prefer another foam for going long.
What’s next?
Where will the shoe industry go from here? The experts we consulted agree that the focus on foam will continue and even more advances are just around the corner. That’s all good news for runners, too, because as foam continues to dominate and brands create increasingly refined rides to match every possible taste, the chances that you’ll find your perfect road partner get better and better.