Shoe educational program: what shoe soles are made of

“What is the difference between TEP and EVA? What does tunit promise me? Is PVC glue? What is the sole of these shoes made of? ”- the modern buyer wants to know everything. In order not to smash his face in front of him and be able to explain whether such a sole suits him in soles, carefully read this article. In it, process engineer Igor Okorokov tells what materials the soles of shoes are made of and what makes each of them so good.

Igor Okorokov - engineer-technologist of shoe production, graduate of Vitebsk State Technological University of Light Industry. Since 2002, he has been working as a specialist in various shoe companies in Russia.

Materials used for the manufacture of soles

The sole is one of the most important parts of the shoe, which protects it from wear and largely determines its service life. It is the sole that is subjected to intense mechanical stress, abrasion on the ground and repeated deformations. Therefore, the materials used for the manufacture of soles should be as resistant to environmental influences as possible. In this article I will tell you what materials the sole can be made of and what are the advantages and disadvantages of each of them.

Outsole Mounting Methods

There are two main methods for attaching soles: glue and injection. But contrary to popular belief, the fastening technology does not affect the consumer properties of shoes. The glue method is used for classic and model weekend shoes, most often on leather or tunne soles. In the manufacture of comfortable shoes for everyday wear, the injection method is most often used.

Soles made of different materials are characterized by different methods of fastening. Soles made of polyurethane are most often made by direct casting, but in rare cases, the pre-molded sole is glued to the top. Soles from TPU are obtained by injection molding at high temperature under pressure. Also made of thermopolyurethane heels. The bottom of thermoplastic elastomer is molded by injection molding, and then glued. PVC soles are most often fixed by injection molding in the manufacture of shoes for outdoor activities and everyday wear. EVA soles are attached to the top of the shoe only by injection molding, and tunit and leather soles are only glued. For TPR, both options can be applied.

Soles made of polyurethane (PU, PU)

Advantages: Polyurethane has excellent performance properties: it is lightweight due to its porous structure, offers good abrasion resistance, is flexible, and has excellent cushioning and thermal insulation. Polyurethane soles are lightweight and flexible, making them ideal for footwear where these characteristics are particularly important.

Disadvantages: The porous structure of polyurethane is also a downside. For example, it causes polyurethane soles to have poor traction on snow and ice, making winter shoes with PU soles very slippery. Another drawback is the material's high density and loss of elasticity at low temperatures (below -20°C). This can lead to cracks in the sole's flex points, the rate at which these cracks appear depending on the wear patterns of the shoe, particularly the wearer's gait, mobility, and other factors.

Polyurethane Soles (TPU, TPU)

Advantages: Thermoplastic polyurethane (TPU) has a high density, making it suitable for producing soles with deep treads that provide excellent traction. TPU also boasts high wear resistance and resistance to deformation, including cuts and punctures.

Disadvantages: The high density of thermoplastic polyurethane (TPU) is also a disadvantage, as it makes the TPU sole quite heavy, while its elasticity and thermal insulation leave much to be desired. To improve these characteristics, TPU is often combined with polyurethane, thereby reducing the sole's weight and increasing its thermal insulation and elasticity. This method is called two-component molding, and it's fairly easy to recognize: a sole made using this technology consists of two layers: the top layer is made of polyurethane (PU), while the bottom layer, which contacts the ground, is made of thermoplastic polyurethane (TPU).

Thermoplastic soles (TEP, TRP)

Advantages: This material can be considered all-season. It is durable, flexible, and resistant to frost and wear. Thermoplastic elastomer (TPE) provides good cushioning and traction. Thanks to the TPE sole manufacturing technology, its outer layer is monolithic, providing strength, while the inner volume is porous, retaining heat. Thermoplastic elastomer (TPE) is recyclable, meaning its use in soles saves resources and is environmentally friendly.

Disadvantages: At high and very low temperatures (above 50 degrees and below -45 degrees), TPE loses its properties, so it is used only in everyday shoes and, incidentally, is rarely used for special footwear.

Soles made of polyvinyl chloride (PVC)

Advantages: PVC soles offer excellent abrasion resistance, are resistant to aggressive environments, and are easy to manufacture. They are often used in home and children's shoes, and were previously particularly popular in safety footwear, as when mixed with rubber, PVC gains properties such as oil and gasoline resistance.

Disadvantages: PVC is used only in the production of casual footwear for fall or spring because this material is heavy and has low frost resistance, unable to withstand temperatures below -20 degrees Celsius. Furthermore, PVC soles do not adhere well to leather uppers, making high-quality leather footwear with PVC soles difficult and expensive to produce.

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Ethylene vinyl acetate soles (EVA)

Advantages: EVA is a very lightweight material with good shock-absorbing properties. It is used primarily in children's, house, summer, and beach shoes, and in athletic shoes as inserts, as it absorbs and distributes shock.

Disadvantages: Over time, EVA soles lose their cushioning properties. This occurs because the pore walls deteriorate, causing the entire EVA material to become flatter and less resilient. EVA is also unsuitable for winter footwear, as it is very slippery and susceptible to frost.

Thermoplastic rubber soles (TPR, TPR)

Thermoplastic rubber is a shoe rubber made from synthetic rubber, which is stronger than natural rubber but no less elastic. However, modern technology allows for its flexibility to be increased using various additives.

Advantages: Thermoplastic rubber has a low density and, therefore, is lighter than other materials. It has no through pores, so moisture does not penetrate it. However, TPR does have surface pores, which provide excellent thermal insulation. Furthermore, TPR, like other porous rubbers, is an elastic material that provides good shock-absorbing properties. Thanks to this characteristic, shoes with TPR soles relieve excess stress on the feet and spine.

Disadvantages: The low density of the material can be both an advantage and a disadvantage. In the case of TPR, this means that the sole made of this material does not offer particularly outstanding thermal insulation properties. Furthermore, in wet and cold weather, the thermoplastic rubber sole is very slippery.

Soles made of leather (leather)

Advantages: Leather soles are used in all types of footwear, including children's, house, and fashion footwear for all seasons. Shoes with leather soles look great and allow the foot to breathe, as they are a natural membrane.

Disadvantages: Leather soles can become deformed when worn in wet weather, and maintenance requires constant use of special sprays and impregnations. Leather has low wear resistance, so preventative treatment is recommended for leather soles, and is essential for winter footwear. Otherwise, the soles will slip on ice and snow, deforming even faster.

Tunit soles (tunit)

Tunite is a rubber with leather fibers included, which is why the second name of this material is “leather fiber”.

Advantages: Tunite soles are similar to leather in appearance, hardness, and flexibility, but perform better: they are virtually wear-resistant and waterproof. These soles can be easily textured, giving them slightly better traction than leather.

Disadvantages: Despite this, shoes with Tunite soles are very slippery due to the material's high rigidity. Therefore, Tunite is only used in summer and spring/autumn footwear using the adhesive method.

Soles made of wood (wood)

Advantages: Wood is an environmentally friendly and highly hygienic material, and wooden soles have a unique appearance. However, recently, plywood has become more commonly used in shoemaking instead of wood. Plywood can be made from birch, oak, beech, or linden, and is easier to machine, molds easily, and is inexpensive. Cork soles are also popular. When working with them, it's important to understand that cork, due to its natural softness, cannot be used as the primary sole material; therefore, cork is used only for decorative upholstery.

Disadvantages: Wooden soles are hard, wear out quickly, and have poor water resistance. Manufacturing such soles requires a lot of material. Cork upholstery is prone to chipping and defects due to the softness of the material.