Shoe sole is the essential part of the shoe that many buyers ignore when purchasing. So, in this article, let’s talk about shoe sole materials!
Today, we want to discuss the shoe sole materials. The article offers eight most popular materials below. For the buying guide, our recommendation is looking first at the materials, and then at the different fastening systems.
We can summarize the latter in the following groups:
- Thermoplastic materials: PVC – TR – TPU
- Two-component polyurethane materials: polyether-based PU – polyester-based PU
- Copolymers: such as rubber and EVA
- Buying shoes, many people look at everything, except the shoe sole materials: Yet the type of material used, the fastening system between the sole and the upper, the tread pattern, and the total thickness can say a lot about the type of shoe you are buying.
Shoe Sole Material Types
The range of materials available to footwear companies for manufacturing the sole is wide. It allows them to give the most appropriate answers to the various needs of quality, cost, and function. They range from natural materials such as leather, rope, cork, wood, and para to synthetic materials. To finish with the combined materials that make up the sole. Here are the main shoe sole materials:
Polyurethane is available in two forms to make shoe soles. Thermoplastic polyurethane is popular for making sports, safety work boots, and leisure shoes. Otherwise, the two-component polyurethane, as the name suggests, is available in liquid form, composed of isocyanate and polyol.
TPR Outsole Definition
When thinking about the material of the shoe soles, many people immediately think of thermoplastic rubber (TPR)? Their most crucial ingredient is the famous styrene-butadiene-styrene (SBS) that can improve performance.
There are other substances, such as mineral fillers. The antioxidants are available from time to time, depending on the use and the manufacturer. The thermoplastic rubber soles are ideal for winter footwear, guaranteeing excellent performance even with low temperatures.
As is ideal for manufacturing soles both applied and for direct injection on the upper, TPR outsoles are compounds whose fundamental component is styrene-butadiene-styrene (SBS) added with oils, polystyrene, mineral fillers, pigments, and antioxidants. Thermoplastic rubbers, if planned correctly, do not have problems of resistance to cold and can maintain excellent flexibility at temperatures much below 0 degrees.
Rubber Sole Material
The thermoplastic polyurethane (TPU) is composed of polyurethane elastomers processed with the techniques of thermoplastic materials. People produce them with the isocyanate addition process and have the elastic characteristics of rubber in a temperature range.
Thermoplastic polyurethanes are perfect for different soles intended for demanding footwear for sport, work, and leisure. Because of their specificity, they require a particular type of formulation according to the mechanical characteristics of the final product.
PU Sole Material
Bi-component polyurethane is available in liquid form and comprises polyol and isocyanate. These products belong to two distinct classes: polyethers and polyesters. The difference between these two membership classes follows the structure of the foam. The Polyether forms a compact superficial skin, and inside the sole, it presents itself with open cells. Polyester has closed cells.
Leather Sole Material
Leather soles are ideal with elegant leather shoes. Among their advantages, there is the high breathability associated with excellent resistance. It offers these characteristics to have an effective sole.
It is unnecessary to resort to significant thicknesses to always have light footwear. Thanks to the peculiar arrangement of the fibers, the leather resists perforation. Finally, despite the stressed breathability, the leather guarantees good thermal insulation.
The leather comprises tiny filiform fibers, grouped into larger fibers, and intertwined with each other according to a three-dimensional design. It forms a system of channels and passages for the air. Its physical characteristics are many, but the most important for its use are:
- Breathability because of the high porosity coefficient
- Low specific weight concerning thickness and surface that in practice translates into lightness
- Significant thermostatic power with consequent thermal protection of the foot
- High resistance to perforation because of the particular asymmetrical arrangement of the fibers, intertwined in a three-dimensional way
- Excellent structure to ensure the electrical balance of the organism following poor insulating power for electricity
PVC Outsole Material
Vinyl chloride (PVC) is one of the most widespread plastics in the world. The manufacturer finds its application in footwear both for boots and for manufacturing soles, sandals, and accessories. Subject to continuous technological development, it has reached a good level of environmental and application efficiency that allows it to guarantee maximum safety in all phases of its life cycle.
EVA Outsole Material
EVA is a polymer composed mainly of ethylene and vinyl acetate. The ratio between the two components and the percentage of cross-linkers, fillers, and expanding agents. We add them to the compound to determine its performance characteristics. EVA is mainly ideal for the production of soles and midsoles. The microporous soles, characterized by lightness, flexibility, and elasticity, come with the propensity to maintain the original shape.
Among the phenomena of the evolution of the sole, there is the combination of materials that respond to stylistic, technical, and cost requirements. All combined with cost containment and the yield of a visually attractive article. The combinations are distinct for the type of materials, colors, and ease of processing. In most cases, polyurethane, rubber, and EVA materials are ideal.
Basic Knowledge about Shoe Soles
The footwear sector offers the market an infinite number of models in different types: slippers, sandals, slippers; sneakers, sports, and leisure shoes. We also have classic footwear for men and women, women’s heeled shoes, shoes for work and sports, orthopedic footwear, safety footwear, children’s footwear, and sneakers.
They involve different processing techniques and have the most significant difference in the system of attachment of the sole to the upper.
The type of sole directly links to the type of processing that the shoe requires. It is possible to distinguish two large groups of sole processing. The first group includes the soles that will be applied directly to the assembled last and subsequently finished. The second one is the pre-finished and monobloc soles. The sole factories prepare them and are ready to be assembled to the upper.
To the category of finished monobloc, soles belong to many soles in rubber or similar materials. We can print them in molds prepared on the templates of the last and do not require any further finishing operation.
The Sole Regulations
Among the various standards in force at the international level concerning the sole, we recall the UNI CEN ISO / TR 20880 of May 2007. We have the performance requirements for footwear components.
The CEN Technical Report shows the performance requirements of shoe soles that must be indispensable for a quality sole. These requirements apply to many soles (excluding finished footwear) regardless of the material to verify their suitability for last use. The standard establishes the test methods used to assess the conformity of these requirements.
Optional Information on the Label
The footwear market, thanks also to online sales and the globalization of trade, is increasingly flooded with shoes from all over the world. Invoices and quality change a lot, but even the most modest value products are increasingly made with a deceptive appearance. It is important to know how to read the labels well to distinguish the type of material used, starting from what the legislation allows and what it prohibits.
It is possible to integrate voluntarily the mandatory information with other supplementary indications as long as they comply with good commercial use, such as indications of the quality of the materials used and the finishes.
The optional information, which must be reported in an official language of the European Union, cannot replace the mandatory information relating to the composition of the product. The optional indications, if applied, must be clear, legible, and truthful and must not mislead the consumer.
- The Vero Cuoio brand signals to the consumer that the material. The material they stamped is leather. It is a voluntary trademark.
- The Vero Cuoio Italiano trademark attributes to superior quality leather, tanned with extracts of vegetable origin and produced in Italy only by the tanneries belonging to the Vero Cuoio Consortium.
- For the attribution of the wording “made in China” to a finished product, the only parameter is the European customs legislation (Community Customs Code REG. 2913/92 / EEC and the application provisions REG. 2454/93 / EEC).
The sole manufacturer can specify the origin of the product by affixing the wording only to the inner part of the sole itself. The wording must be in Italian or in another official language of the Community (Ministerial Decree of 30 January 2001).
The Duties of the Manufacturer
They required the manufacturer or his representative based in the European Union to provide the label and handle the accuracy of the information contained. It must also show the identity and contact details of the producer and information to trace the origin of the products (e.g. product code).
If neither the manufacturer nor the representative follows the territory of the European Union, the obligations stated above are the responsibility of the first community commercial operator. The retailer must take care to verify the label on the footwear he sells. We must ensure the display in the places of sale to the ultimate consumer and the sign illustrating the symbols prescribed by the legislation.
The Ministry of Economic Development carries the functions of market surveillance authority out. It exercises them with the help of the Chambers of Commerce and possibly the collaboration of its territorial offices, as well as the collaboration of the Guardia di Finanza. The territorially competent Chambers of Commerce carries the ascertainment of violations of, as well as by the Customs and Monopolies Agency and by the officers and agents of the judicial police.
The territorially competent Chambers of Commerce imposes administrative sanctions. The surveillance activity is carried out by a visual-formal check or sample analysis and can be carried out on the footwear present at production and distribution sites.
How Soles are Attached to Shoes?
Sometimes, we hear about sewn, vulcanized, or injected soles. But what are we talking about? It is the method that attached the soles to the shoe upper. Sometimes, for example, they are simply glued, using a mastic compatible with the material used for their production.
At other times, hand sews or by machine, while at other times we vulcanize the soles. We also used this term in promotional messages. It testifies to the fact that we weld directly the sole on the shoe upper, through the use of suitably heated molds.
It is always worthwhile to focus on their sole when buying new types of shoes. Trekking or hiking shoes will have to meet certain requirements. The important thing is to have enough basic knowledge to understand what you have in your hands!