Read more: The best running shoes for any budget in 2021Р”В¬reating a new type of yarn for the upper wasn't the only issue. 'At the start of 2017 we were able to make shoes and components in repeat, before that we had only been able to make one or two shoes at a time,' Sahanga says. Before this, adidas didn't have one material that it could use to create an entire shoe РІР‚вЂњ traditionally, the uppers of running shoes are made from polyester. 'TPU yarn is available on the market but we have developed one specific for us and have advanced it,' Sahanga explains. The breakthrough in the project, which has been running for six year, came in 2016 when engineers modified the plastic so that it could be spun into a traditional fabric-style strand. The problem for her team was that while the TPU can be manipulated into a midsole relatively easily, turning it into a thread that can be used to create a shoe's upper is far more challenging. (It's an off-white colour because there's no brightening chemical that usually gives trainers a pristine white look, she says). 'The upper is made from exactly the same material,' Sahanga says of Loop. When used in a midsole, Boost is formed of 2,500 elastic TPU beads that are pressed into a mould to create an unmistakeable rice cake look. This isn't the first time the company has used a variant of TPU within its shoes in February 2013 adidas introduced its Boost foam, which is used in the majority of its midsoles, after working with German chemical producer BASF. TPUs are one type of the plastic polyurethane and is considered to have elastic properties, as well as being transparent, and largely resistant to oil and grease. Once they arrive here the material is ground down into fine pellets, then melted back to its original state from which it can be turned back into a shoe again.Р”В¬rucially, TPU can be melted down once it has been used. To recycle the shoe, adidas has them washed and shipped to one of the plants of its industrial partner ASF.

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