There used to be such a metaphor: Suppose a shoe is regarded as a car, the outsole is the wheel, the midsole is the suspension system, and the upper is the body. When the vehicle is driving, when encountering complex road conditions, if the suspension system is not good, the driving comfort will be impossible, especially the shoes. Whether the soles of a pair of sports shoes are comfortable or not depends on the middle layer. The quality of the midsole of the shoe is not good enough, and the shock absorption capacity is weak, which may damage the body. Therefore, the midsole is the essence of a pair of sports shoes, and it is also the most technical part of sports shoes.
So here comes the question: What material are the midsoles of most trendy sports brands made of?
EVA (Ethylene Vinyl Acetate Copolymer)
Speaking of which, you must be very curious, where is EVA sacred? Come, watch videos if you have traffic, and watch videos if you don’t have traffic!
EVA material is a polymer compound formed by the copolymerization of ethylene (ET) and vinyl acetate (VA) through a high-pressure bulk polymerization process. After density polyethylene (LLDPE), the fourth largest ethylene series polymer. As a rising star, it has the characteristics of excellent performance and a wide application range.
In terms of product performance control, EVA mainly depends on changing the process conditions (reaction temperature and pressure), the injection amount of regulators, and the injection amount of vinyl acetate (VA) to control the melt index (MI) and vinyl acetate (VA) content of the product, to form different grades of products, used in different directions.
In the production of EVA devices, if the MI is kept constant and the VA content is appropriately increased, the elasticity, softness, transparency, environmental stress crack resistance, and filler compatibility of the product will also be improved; conversely, when the VA content is reduced, its The performance of the product is close to that of polyethylene, and the rigidity, tensile strength, abrasion resistance, chemical resistance, heat resistance, and electrical insulation are improved. If the VA content is kept constant and the MI is increased, the softening point will decrease, and the processability and surface smoothness will be improved; on the contrary, if the MI is decreased, the molecular weight will increase, and the impact performance and environmental stress cracking resistance will be improved. Therefore, manufacturers can choose the corresponding brand of EVA according to product needs, market demand, design concepts, etc.
Stable chemical properties, the backbone of shoe materials
◆ EVA is an ethylene product with stable chemical properties, and the VA molecular group in the molecule is resistant to oxidation and chemical corrosion. Therefore, the overall chemical properties of EVA materials are stable, and to a considerable extent, resistant to seawater, grease, acid. , alkali and other chemicals corrosion. Because of this, it has a long service life, is antibacterial, non-toxic, odorless, and non-polluting, and is a rare environment-friendly material.
◆ The vinyl acetate monomer is introduced into the molecular chain of EVA, which reduces the crystallinity and improves the elasticity, flexibility, impact resistance, filler compatibility, heat sealing, transparency, and other properties.
Therefore, in terms of shoe materials, EVA materials are better than other vinyl products and become the mainstay of the midsole of sports shoes.
Strong blending ability, excellent comprehensive strength
Compared with other excellent polymer materials, EVA has a better “blending” ability due to its special molecular structure. A new type of modified material (commonly known as “polymer alloy”) formed by EVA material as the main body and other polymer materials as modified components have the advantages of various polymer materials, making the original excellent EVA material in performance. up again.
EVA blended derivatives have excellent performance in thermoplastic elastomer materials and have the characteristics of elasticity, flexibility, shock resistance, wear resistance, corrosion resistance, environmental stress crack resistance, and water resistance, making it a trendy brand The perfect choice for sports, training, and casual sole materials.
At the same time, manufacturers will use different injection molding technologies for functionally modified materials according to their needs and introduce different functional shoes for selection.
Lunar (EVA and nitrile rubber blend)
Lunar, one of the EVA hybrid derivatives. 30% lighter than EVA and Phylon. Using this material to make the midsole of the shoe can make the overall weight of the shoe lighter. At present, the main object used is the Lunar series running shoes in NIKE shoes.
Phylon (secondary EVA foam material)
Phylon, a secondary EVA foam material. Compared with EVA, Phylon is light and elastic and has good cushioning performance. The classic Air Jordan 10 midsole uses Phylon. At present, most of NIKE’s basketball shoes also use a Phylon midsole.
Phylite, made of 60% Phylon and 40% rubber. Phylite is lighter than rubber and heavier than Phylon. Running shoes using this material are characterized by lightweight and flexibility. At present, the main objects used are the FREE RUN series in NIKE shoes.
Fresh Foam (EVA modified material)
Fresh Foam, modified from EVA. Compared to EVA, Fresh Foam is more precise, softer, lighter, and more shock-absorbing. At present, most New Balance casual shoes use the midsole of Fresh Foam material.
Probably because EVA is too good, it is applied to various products.
◆ Film materials such as functional shed film, inner film of food packaging, special film for photovoltaic power generation applications;
◆ Optical cable, electric wire, and cable anti-leakage sheath;
◆ Hot melt adhesive, functional adhesive;
◆ High-end instrument panels and interior parts of aircraft and automobiles;
◆ EVA can be seen in civil construction boards, medical equipment, and other medical supplies for people’s livelihood.
Today, EVA material has become one of the indispensable excellent polymer materials in the petrochemical product market.