SCF foam injection moulding


Diagram: Trexel


USA. The ability to produce midsoles and outsoles in a single step is a “really, really different way” of working for the shoe industry, said Murielle Guillot, Footwear Materials Offer Manager, at Decathlon. The sports and active wear group has worked with partners in recent years on a patented SCF process that has culminated in the Kiprun KipX running shoe launched in April. This is described on sales sites as “the first adhesive-free shoe that revolutionises the manufacturing of running shoes to enhance performance with its softer cushioning and increased responsiveness.” Guillot explained the problem Decathlon


was addressing: that EVA-based foam sole manufacturing is labour-intensive, uses chemical foaming and prevents recyclability. The midsole and outsole are produced separately, then bonded with glue during the stock fitting stage, before assembly with the upper. In turning to a SCF foaming process, the objectives were to reduce 20 production steps to just one, she told the audience at the conference (which was organised by AMI, publisher of TextilesLoop). In comparison tests with EVA, the TPU SCF foam sole showed excellent cushioning performance and durability. The new process also enabled a big improvement in the manufacturing element in a Life Cycle Assessment, she said.


The four main steps of Trexel’s MuCell process for supercritical fluid (SCF) foaming are: 1. As thermoplastic pellets are plasticised in the machine’s barrel, precise amounts of SCF, typically nitrogen or carbon dioxide, are introduced into the melt. 2. Homogeneous mixing and dispersing of the SCF in the polymer melt creates a single-phase solution. 3. This is injected into the mould cavities and cells start to nucleate once exposed to lower pressure there. Molecular dispersion of the SCF leads to a homogenous closed cell structure. 4. The usual holding and packing phase is replaced by controlled cell growth which ceases once the cavity is filled.


SCF advantages One of Decathlon’s partners is shoe manufacturing machinery group Tien Kang. Will Huang, Innovation Director, said at the conference that the Taiwan-based company started work with the SCF process in 2016. “What attracted us was the clean and chemical-free nature of this process,” he said. Because SCF is a physical foaming process, there are no chemical foaming and cross-linking agents, he said. Other advantages over chemical foaming include 1:1 foam injection and recyclability. Tien Kang developed its Gentrex physical


foaming injection moulding machine with partners Trexel from the USA and FCS from Taiwan. Other shoe brands it has partnered are K2, which uses SCF with TPU, and Aloft, which is applying the technique to Pebax foam. “We have been asking, what more can


we do with this technology?” said Huang. Sharing Tien Kang’s development work, he


Shoe sole manufacturer Aloft, based in Portugal, says it is the first in Europe to be mass- producing soles using a SCF foaming process. Its website says production capacity of its E-Blast soles is 500,000 pairs per year. Image: Aloft


26 Textiles Loop • Autumn 2025


showed a diagram of a highly automated production system called Gentrex Fusion Pro, and another system named Gentrex Gemini for producing dual colour, dual density foams. Tien Kang has set up an Innovation Centre in Taiwan where customers can view its development work, which includes potential “lights-out” manufacturing with robots. Trexel is a key IP owner in physical


foaming injection moulding and the company’s CEO and President, Levi Kishbaugh, also spoke at the Polymers in Footwear conference. Trexel has been successful in implementing its technology in many industries and has been promoting its use in the footwear production chain for more than 10 years. “What’s changed now,” said Kishbaugh, “is that footwear brands are showing interest.” For footwear companies, the challenge is


knowing how to design for SCF-based production, he said. The answer is software simulation, a service which Trexel offers and Kishbaugh introduced in his presentation that covered process and design considerations such as foam expansion, cell size, density and mould filling.


Bio-based isocyanate Sustainability through recycling is one area of innovation for shoe soles; another is the development of bio-based materials. In October, Cirql expanded its “zero” collection with Cirql Zero36 midsole foam made from


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34