The foam also has good "rebound performance and outperforms expanded grades of polyethylene and polypropylene,” he added. The material will also outperform ethylene vinyl acetate, which often is used as a layer in the soles of running shoes.
The material is being used by German sports shoe maker Adidas. The firm’s senior innovation director Gerd Manz said that runners want good cushioning in an insole – one that "lands kinetic energy" upon touchdown.
In their first three months on the market, Energy Boost shoes sold 250,000 pairs, making them one of Adidas' most successful launches, according to Manz.
Infinergy was inspired by the lightness, elasticity and rebound of a tennis ball, according to BASF research chemist Frank Prissok.
The innovation pivots on the cushioning properties that stem from a solid granular TPU made into thousands of small energy capsules, or TPU pebbles, inside the shoe’s midsole.
Tests conducted by Adidas show the material “provides the highest energy return in the running industry,” the firm said.
Prissok added: “Infinergy is the first expanded thermoplastic polyurethane (E-TPU). It is a closed-cell elastic particle foam consisting of individual beads.
“The individual particles of 5-10-mm in size are pressed and fused against one another in the manufacturing of parts. It is particularly lightweight - bulk density - 100g/l - very elastic, tensile and stretchy.
“The foam has high long-term durability and outstanding resilience – better than EVA (ethylene vinyl acetate), which has previously been used in the majority of sports shoe midsoles,” he added.
The technology was developed using BASF’s Elastollan. BASF opened new facilities to produce the TPU material in Shanghai in 2014.
Eric Liedtke, global head of brands at Adidas predicts the sale of 15m pairs of Boost sports shoes globally by the end of 2015. He said: “Boost cushioning foam provides the highest energy return in any running products.”
Going for the cup
Soccer boots are a large part of the sports footwear market and Bayer’s Bayflex polyurethane was used in Adidas’ Samba Copa Mundial boots in the 2014 world cup.
Used in the manufacture of microcellular polyurethane innersoles and midsoles, Bayflex 962 is a fully compounded polyether-based polyurethane system consisting of a modified MDI pre-polymer and polyether polyol system.
BMS said: “Units prepared from these components combine light weight, comfort, and durability.”
The Samba Copa Mundial is “particularly lightweight, robust and comfortable with an outsole is that is constructed of dual-density direct injected polyurethane and moulded studs,” according to a BMS press release.
Also in the last world cup, Pebax polyurethane elastomers from Arkema were widely used in Puma football boots.
French company Arkema said that the sole plate, the padded areas of the boot and reinforcing strips contain a foam made from the elastomer.
Arkema said that the polyurethane was chosen for Puma’s evoPOWER boots because of its combination of low density, durability, strength and resilience.
The daily grind
Work boots may not be as glamorous as soccer boots, but they are an equally demanding application.
While Huntsman has its own brands of sole materials, the firm recently teamed up with work boot producer Panter to improve its soling capacity.
Panter has a shoemaking facility in Alicante, Spain, which operates 24 hours a day, six days a week.
The firm recently worked with Huntsman technical experts to move production into TPU for the soles for a range of its professional safety boots.
According to Santiago Anguera, sales manager ACE, Footwear and TPU Iberia at Huntsman, “performance-wise, the material achieves shorter cycle times as well as good abrasion and slip resistance.”
“When it comes to looking after the comfort and safety of employees at work, particularly those that spend all day on their feet, it’s imperative to make the correct footwear decisions,” added Anguera.