GOT SOLE? THE DNA OF THE MIDSOLE
Understanding the Most Important Technology in Running: Cushioning
Every day, running shoe manufacturers are looking for the next innovation. When it comes to proprietary technology, foams have been a driving force in this race, and the midsole is the anchor, where the cushioning layer of foam resides under the insole and above the outsole of running shoes. Consider the new kids on the block – Boost, EverRun, FlyteFoam, Fresh Foam and ZoomX, to name just a few. These new formulations were created to not only absorb shock but also to provide support and extend the comfort of the overall ride. So how have midsoles changed? For the runner, it’s about having a shoe that will move with your foot.
Today’s midsoles are the result of an evolution of foams. There are many polymers that can be thrown into the mix – let’s start with the basics. EVA, which stands for ethyl vinyl acetate, is a type of copolymer foam that’s been used in the footwear industry for well over 40 years. When evas were first introduced, they were much less durable and less energy efficient than the compounds used today. “Over the last few decades, shoe manufacturers have experimented by adding different polymers,” says Brice Newton, who works in Brooks’ global footwear division. Spencer White, V.P. of Saucony’s Human Performance and Innovation Lab in Lexington, Mass., explains, “The biggest improvements made to the foam composition also made the shoe lighter, bouncier and more abrasion resistant, so they don’t need to use as much rubber on the bottom of the shoes, which again makes for a lighter-weight shoe.”
Now for as long as there have been evas, there have also been polyurethane (PU) foams. These are much more durable than evas but also much heavier with almost the same amount of bounciness or energy efficiency. As an example, some PU foams, like memory foams, of which some mattresses are made, have very poor energy efficiency. This means when you push on them, they retain that shape. “That’s not good for a running shoe because you want the shoe to recover and be ready for your next step,” says White. “It would be best if it could recover just as your foot is lifting off the ground to give you a little of that energy back that you put into it.”
There are other drawbacks to the poured PU foams. Since they are open cell foams, they absorb water and break down very easily. eva is a closed cell foam and is more durable but not as bouncy as shoe manufacturers would like.
To a runner, a durable shoe is important because it maintains its ability to protect the runner better. Because eva breaks down steadily, after you put in a few hundred kilometres in the shoe, you’re not getting the same kind of cushioning as you did during that first run.
EVA midsoles also change over the course of a single run. Because these foams are not 100 per cent energy efficient, with every step, you’re leaving a little energy in the midsole. Every time you land, some of that energy stays inside the centre of the foam and gradually over time heats up. White says that if you took a temperature probe and stuck it in the centre of the heel of a running shoe and then go for a run on a 21 C day, after less than 5k, the temperature in the centre of that heel could be over 50 C. eva gets significantly softer when it heats up, meaning that over the course of a run, the midsole gets softer and less able to absorb the impact compared to the beginning of the run. Of course, when runners get fatigued at the end of the run they need cushioning. So it’s good to have a shoe that can still do it for you.
Enter a new class of foams called Polymer Bead foams, specif ic a l ly Expanded Thermoplastic Urethane (etpu).
“We’ve been looking for a long time for foams that can overcome some of these earlier problems, and we ran across a new class of foams called Polymer Bead foams, and that’s what this expanded tpu foam is,” points out White. “What’s different about everun is the base polymer and the manufacturing process we’re using. But what’s interesting is that these expanded tpu foams are much bouncier, much livelier, more f lexible than eva materials and much more durable and less temperature sensitive.
“So everun is an etpu foam that maintains its cushioning properties about three times longer than eva. So it’s still breaking down over time but much less dramatically. And because it’s so energy efficient and not very temperature sensitive, it maintains its ability to protect runners at the end of their run better than eva,” says White.
New Balance Fresh Foam Hexagons and 3D printing
The composition of the foam isn’t as important as how the foam is being shaped using 3d printing, which you can check along the sides of the shoe. In the case of the Fresh Foam, hexagon shapes will either be concave going in a pocket or convex sticking out and, depending if it’s a running shoe, training shoe or trail shoe, the hexagons will have a different configuration. “In the most general sense, the lateral sides of a Fresh Foam side wall will be concave, says David Korell, footwear merchandiser for New Balance Canada. “So if a runner lands laterally on the heel or supinates, the foam is going to compress more into that concave pocket. And as the foot naturally pronates, that convex pocket is intended to be a bit firmer when it’s loaded with weight. So we can tune the midsole without having to add plastics or gels to do different things heel-to-toe, just based on the shape of the hexagons.”
The long-term goal is for a consumer to stand on a scanning device that would send information about their foot to a 3d printer so that a shoe could be created specifically for their individual mechanics. Last year, 44 pairs of 3d-printed Fresh Foam shoes were produced and sold commercially for a limited time for us$ 400 each as a test project.
Brooks BioMoGo DNA
“We’re using what we call BioMoGo dna; it’s unique and proprietary to Brooks, and we’ve also recently launched Super dna. Both are different forms of eva,” says Newton. “For the BioMoGo, we’ve used an additive in the eva that allows it to break down, which makes it completely biodegradable, unlike other evas. The second part is the adaptability of our evas. Brooks dna uses a non-Newtonian f luid that has a consistency t hat is tot ally dependent on the stress applied. So no matter your weight, how you run or where you land, that midsole material will adapt to whatever load you apply to it.”
Thinking of breaking the two-hour marathon? Well, that’s what Nike is hoping its new Nike Zoom Vaporf ly Elite with the new ZoomX midsole will do. And although you might not be ready to break this barrier, Nike has included this ZoomX midsole in the Nike Zoom Vaporf ly 4%.
Nike describes the ZoomX midsole as a system that provides responsive cushioning that allows the runner to maximize on speed and benefit from a greater return of energy, without increasing demand on the calf. “The groundbreaking new Nike ZoomX midsole and curved carbon fibre plate work together to provide responsive cushioning and minimized energy loss at toe off,” says Tony Bignell, VP of footwear innovation. Now the Vaporf ly 4% may not have all the innovative bells and whistles of the Vaporf ly Elite, which is custom designed for only their elite marathoners. However, Nike says the performance-driven design of this running shoe makes it 4 per cent more efficient than its previous fastest marathon shoe. And when it comes to the design esthetics, Nike has taken the idea of looking fast to a whole new level. The striking aerodynamic heel counter, along with the Flymesh upper with its midfoot wrap, seem to make the foot and shoe f it seamlessly toget her as one unit .
Asics uses many different foams, depending on the runner’s need, price point and even the production process. “If the focus is to create something lightweight or with more bounce, then we would look for a specific kind of foam that would deliver these features,” says Asics’s Jork Geraets, global product line manager. “One of our foams is called Speva, and it has really great bounce and a comfortable feel, perfect for the recreational runner but it’s not the lightest weight. So it wouldn’t be the foam
we would use if we are creating a fast shoe for a sub- three-hour marathon.”
Asics’s answer to t his is FlyteFoam. Geraets explains that if you want to make the standard midsole foam lighter, you would blow up the cells of the foam more so the cells will get thinner. This makes it lighter, but it’s also less durable and has less shape retention. “With FlyteFoam, we added organic microfibres and Kevlar fibres to the compound that help strengthen the cells and make the midsole very strong. So it’s super lightweight, more durable than eva and will perform longer, as it has good shape retention. This means the runner will get the same cushioning every single mile.”
As for the future, Geraets believes the development in foams will continue since we’re always looking to improve the weight and the ride of their shoes. “We are already prototyping FlyteFoam 2.0.”
Based on a groundbreaking development process created by Adidas partner basf, the world ’s leading chemical company, solid granular material ( tpu) is popped like popcorn in a streaming process and expanded into thousands of small energy capsules, which make up the footwear’s distinctive midsole. With their unique cell structure, these capsules store and unleash energy more efficiently.
Head of design for sport performance James Carnes told Sole Collector when Boost was introduced, “Traditional shoes using a foam-based cushioning utilize one large piece of foam. The Boost platform has taken an entirely different approach – individual capsules. These little capsules are moulded together, and they retain their normal properties better than any material out there. They’re able to absorb energy, and then unleash that energy at a consistent rate, over and over.” The other feature of Boost is that it’s not temperature sensitive.