EVA vs ETPU-interpretation of shoe midsole materials
EVA: The backbone of the shoe material field
eva foam block supplier in China – Ideastep
EVA is a random copolymer composed of ethylene and vinyl acetate, in which vinyl acetate (VA) is used as a flexible segment in the EVA molecular chain, and ethylene is used as a crystalline segment, which shows a certain degree of softness and high elasticity as a whole.
In terms of technology, EVA in the shoe industry generally adopts chemical in-mold foaming. The EVA pellets are put into the foaming mold, and high temperature and high pressure are applied to foam. Foaming EVA can make the sole lighter, and the EVA resin with a certain degree of elasticity allows the sole to have a proper cushioning function, so that the EVA foam shoe material can adapt to the needs of most casual shoes and jogging shoes. The resilience of EVA after foaming can generally be increased to 50-55% or even higher.
EVA blended foam products are widely used in the soles and interior materials of medium and high-end tourist shoes, hiking shoes, slippers, sandals. And because of the price advantage of EVA foam material, it will still be the main material choice for popular sports shoes for a long time in the future.
ETPU: epoch-making foam shoe material
TPU, or thermoplastic polyurethane elastomer, is a block copolymer composed of diisocyanate, chain extender, and polyol. Among them, the soft segment composed of polyols exhibits flexibility and toughness, while the diisocyanate acts as the hard segment, giving the material hardness and rigidity, and the hard segment is crystallized as a physical cross-linking point, making the TPU exhibit high elasticity. Therefore, TPU has significant advantages such as high tensile strength, high elongation, and low long-term compression set rate.
In terms of technology, the ETPU midsole adopts physical foaming. Compared with the chemical foaming of EVA, it has no taste and is environmentally friendly and recyclable. The slippery performance is also far beyond the traditional EVA material. The foamed TPU is ETPU, and the rebound value of the foam falling ball can reach 60%, which is significantly higher than that of EVA. It is equivalent to the rebound of the shoe when it hits the ground, which can effectively reduce muscle fatigue and reduce muscle jitter, allowing you to run farther with full power~
However, the price of ETPU is higher than that of EVA, which discourages some manufacturers, and there are certain difficulties in process innovation. But these are temporary. Many manufacturers have tried to bring ETPU materials to a wider range of downstream applications. For example, the successful commercial application is the ETPU plastic runway. In recent years, more commercial applications have appeared in our In the field of vision, such as ETPU bicycle cushions, sports protective pads, ETPU child crawling pads, bicycle helmet padding, car seat padding, and so on.
In general, the price of ETPU is higher than that of EVA, but ETPU is much better than EVA in terms of resilience, deformation recovery, abrasion resistance, and wet resistance. And most importantly, ETPU is environmentally friendly. The big trend. Therefore, to use good materials as the midsole of good shoes, but also to consider the appearance of the shoes, soft and hard comfort and other conditions, then the expensive shoes can be imagined~
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