Work shoe sole material types

Sole material types: Rubber (RU), Thermoplastic Rubber (TR), Polyurethane (PU), or Thermoplastic Polyurethane (TPU) Cowhide sole (wear-resistant)
Polyurethane
The simplest shoes are made with a single-density polyurethane outsole. Polyurethane soles must perform two tasks: first, they must be comfortable and lightweight; second, and very importantly, safety aspects such as anti-slip. In fact, it is difficult to combine these two functions, and in most cases, only one function can perform correctly. The density of polyurethane soles is mostly around 0.8g/cm3, usually used in the leisure footwear industry. The production of single-density shoes is simple and efficient, but the products are still high-end commercial shoes.
Polyurethane/Polyurethane
For over 20 years, the footwear industry has been producing double-density polyurethane shoes using directly injection-molding machines. The combination of a dense polyurethane outsole and a lightweight and comfortable midsole makes it possible for shoes to combine two characteristics. A highly dense material can be used to make the outsole, giving it greater wear resistance and good anti-slip and oil-resistant properties. A foamed polyurethane system can be used to make the midsole, making the shoes more comfortable and even lighter. The shoe making process differs from that of single-density shoes. First, the dense outsole is injected into a closed mold. After a certain reaction time, the midsole and the upper part of the outsole are injection-molded. Through the bonding of the sole and the upper, a simple shoe sample is successfully made. In most cases, this type of material combination is used in the safety footwear industry because this industry seeks both comfortable appearance and superior properties. However, many interesting designs using polyurethane/polyurethane material combinations can also be found in casual footwear. The density of the dense outsole is mainly 0.9g/cm3, while the density of the midsole is mostly 0.45g/cm3.
For safety shoes, two-layer bonding exceeds the required standard, and the midsole can be made with a thinner layer.
Thermoplastic Polyurethane
This type of material combination is not as advertised, because a single-density thermoplastic polyurethane outsole will not make the shoe much more comfortable. The density of thermoplastic polyurethane is around 1g/cm3, which means that this type of shoe will not have good sound insulation for footsteps. In addition, bonding thermoplastic polyurethane to the upper is often very difficult, so thermoplastic polyurethane outsoles are not often used.
Thermoplastic Polyurethane
Thanks to new advances from material suppliers, this type of shoe is becoming more interesting. Thin thermoplastic polyurethane outsoles and blown thermoplastic polyurethane midsoles will become a new material combination in the future. More or less, its principle has something in common with the polyurethane/polyurethane production material combination method. The hardness of thermoplastic polyurethane covers a wide range. In the footwear industry, the Shore hardness ranges from 55A to nearly 85A. In fact, it has excellent wear resistance and anti-slip properties, and thermoplastic polyurethane gives the sole excellent carving craftsmanship. Blown thermoplastic polyurethane can be injection-molded, which means that manufacturers can skip the production material combination method from thermoplastic polyurethane to thermoplastic polyurethane/thermoplastic polyurethane. In terms of processing, thermoplastic polyurethane has great advantages compared with polyurethane. Thermoplastic polyurethane can be bagged and granular when fed. It does not involve chemical expertise, and operators do not have to adjust a large number of parameters for different machines when operating the machine.
Thermoplastic Polyurethane
This may be the most commonly used material combination today. Thermoplastic polyurethane/polyurethane has many advantages. First, the shoemaking process can be completed through a one-stop process. In this process, thermoplastic polyurethane is used to make the shoe outsole, and polyurethane is used to make the shoe midsole. For direct molding of the bottom, it is interesting to combine the shoe outsole made of compact thermoplastic polyurethane with the low-weight shoe midsole made of self-reactive polyurethane foam. The result of the combination produces a composite sole with a highly wear-resistant outsole and a comfortable midsole. In addition to their outstanding physical properties, thermoplastic polyurethane shoe outsoles can meet the needs of modern design, using transparent or brightly colored soles during direct molding.
Multifunctional Thermoplastic Polyurethane
Using a thermoplastic polyurethane injection molding process, the new DESMA process can produce three-color soles, which excites designers and manufacturers. This allows for a one-process, three-color or functional approach. Colored materials are injected into the channels within the mold frame by a pair of injection molding equipment and filled upwards to the sole area, with the injection amount determined by the user. After curing, the injection material forms the outsole. Then inject the midsole to complete the production. All operation steps are completed on the same machine, as part of the same overall process. Untreated, it cannot be sold. This not only saves processing, distribution, and material steps, but also improves product quality and economy. One process, multiple sole properties, the DESMA process quickly utilizes the uncertain characteristics of new products, and the soles can be distinguished not only by color, but also by different hardness, function, strength, and properties.
For example, these advantages allow safety shoe manufacturers to offer shoes with special category support functions or that make it easier for users to walk.
Rubber/Polyurethane
One of the best material combinations is to use rubber for the outsole and polyurethane for the midsole. The outsole and midsole of the sole can be made step by step, and finally bonded together using an adhesive. In most cases, pretreatment is required, such as halogenation and/or polishing of the rubber surface. Another bonding method is to use non-woven wool between the two materials, using the mechanical bonding function of rubber and the bonding function of polyurethane to achieve the bonding purpose.
However, all these processes involve a considerable amount of auxiliary equipment and a large amount of logistics work. Many footwear manufacturers try to avoid this cost-intensive investment and instead use other easily processed materials. Normally, rubber and polyurethane will not bond due to their different physical and chemical properties. In addition, polyurethane is usually not processed under the predictable conditions of this process. DESMA has therefore developed a process that does not use the above process steps. Today, it can use a combination of rubber/polyurethane materials and produce shoes that do not require any harmful adhesives through a one-step process. Subsequently, the polyurethane injection molding equipment can add a water-based adhesive while injecting polyurethane onto the rubber outsole, bonding the two different materials and meeting the requirements of relevant safety shoe standards.
Rubber/Rubber
One of the most commonly used processes in military shoe manufacturing is the process using a rubber/rubber material combination, in which both the outsole and midsole of the shoe are made of rubber. The outsole is a dense outsole, the same as the process using a thermoplastic polyurethane/thermoplastic polyurethane material combination, and the midsole is made of foam rubber. These shoes are resistant to high temperatures, oils, and fuels. Like polyurethane, these materials do not support hydrolysis, but the situation is different in the military industry, where rubber/rubber military shoes are used. The same is true in the athletic shoe field. This material combination has many significant advantages, such as truly good anti-slip performance.