Material Matters: High Frequency Welding (Hyperfuse)
People use the term seamless to compliment something perfect or executed with precision. It’s no surprise that the masterminds of the sneaker biz would cotton onto the idea at some point, and find a way of producing shoes sans-seams. The footwear engineering fraternity found a way of tapping into some good vibrations, and the advantage of removing the stitched overlaps was realised.
The technology behind the technique goes all the way back to the 1940s – back when scientists were hard at work figuring out how to win the war with advanced tech. There were lots of new ideas and a bunch of research was conducted with radio frequencies, exploring ways to harness their energy for new purposes. Of course, the ability to weaponise frequency and create some kind of microwave heat gun was a top priority, but a less destructive – and ultimately far more beneficial – discovery was high frequency welding. The process has been refined over the years, but at the heart it remains unchanged.
High frequency welding uses molecular friction, which causes plastics to heat up and stick together. Pieces that need to be joined are put onto the table of a powerful press, and then with extreme pressure a die – a kind of welding pattern – is lowered onto the materials, specifying the areas that are to be joined like a map of the weld. When the press comes together the machine passes high frequency waves through the material sandwiched between the table and the die, jiggling the molecules around so that they rub against each other until they get hot. The combination of penetrating heat and pressure produces a precise and incredibly strong weld, fusing the pieces together so they become one. The process is a lot faster than traditional heat joining methods, so it’s ideal for companies like Nike (who call it Hyperfuse) or New Balance (FantomFit) to factor into their production.
Shoes are traditionally made with layers of materials that are overlapped and stitched; the resulting seam creates a weak spot that can be double the thickness of the surrounding area. Seams can rub on and irritate an athlete’s foot, and they’re often the first part of a shoe to break. When materials are joined with high frequency welding they are stronger than the surrounding areas and can even be thinner, due to the compression they’ve endured. The technology allows shoe manufacturers to blend the qualities of sturdy, durable hiking styles with the lightweight performance qualities of athletic footwear. You can see these kinds of properties mixed together to create a new wave of heavy-duty athletic footwear, such as the New Balance Trailbuster Reengineered, adidas Ultra Boost ATR, Nike Air Max Zero and FILA Overpass 2.0 Fusion.
Although it’s only possible to weld plastics with this high frequency technique, there are a lot of different types that can be used. Sheets of PVC and TPU are the most common, but it’s possible to weld EVA and nylon – this means that a solid protective layer can be laminated over breathable mesh. You’ll see this employed a lot in the sneaker world to protect toes and strengthen sides. There are endless iterations of material combinations out there that can provide an incredibly lightweight, strong and slim piece of engineering.
Beyond the structural advantages welded construction, it’s opened up a new world of visual possibilities for designers. The 2012 release of Nike’s Hyperfuse ‘Olympics’ pack had people scratching their heads – the way the translucent yellow and blue overlapped to create green brought some new science to the game. Styles that have been heavily layered can now be slimmed down to create streamlined versions of old favourites, as with Nike’s Air Max 95 SE, or to sure up other new tech, as with the mudguard on the Air Max 1 Flyknit.
The quest for lightweight, strong, slim and supportive footwear will continue into the future. As long as there are clever people in the world there will be new ways, but until we can cop graphene rebuilds of some as yet unreleased Yeezy, then we reckon high frequency welded uppers are the best thing around.
Material Matters is our weekly tech section, where we take a peek behind the mesh curtain and break down the building blocks of the industry. Recently, we’ve looked at 3M Scotchlite, vulcanised rubber soles and neoprene.