TPU: Thermoplastic polyurethane characteristics and advantages in the production of shoe soles

What is Thermoplastic Polyurethane?

Thermoplastic polyurethane (TPU) is a polymer formed by the polycondensation of an isocyanate with a diol. The chemical nature of this chain influences the mechanical behavior and chemical resistance of the material: the longer the chain, the more the material assumes characteristics similar to natural rubber.

Like all thermoplastic elastomers, TPU is elastic and melt-processable and can be used on extrusion, injection molding, blow molding and compression molding equipment.

TPU Properties

TPU is one of the most resistant compounds to oils and abrasion, and is impermeable to water and gas. Its excellent elasticity and exceptional elongation ratio guarantee durability and resistance to tears. In addition, TPU oxidizes less easily in air than hydrocarbon-based rubbers. TPU is an extremely versatile material: more than any other thermoplastic elastomer, it can provide a considerable number of combinations of physical properties, making it extremely flexible and adaptable to multiple uses. This versatility comes from the unique structure of TPU which results in high resilience, as well as resistance to impacts, abrasions, tears, atmospheric agents and hydrocarbons. TPU offers flexibility without the use of plasticizers, as well as a wide range of hardnesses. For these reasons, TPU bridges the gap between rubbers and plastics: its range of physical properties allows it to be used both as a hard rubber and as a soft thermoplastic material. TPU can be sterilized, welded, colored, painted, printed, die-cut and cut; it is flexible at low temperatures and in some conditions shows biocompatibility, hydrolytic stability, optical clarity, flame retardant and antistatic properties. Its use is recommended for pipes, gaskets, cables and wires, for technical clothing, for footwear and for all those applications where it is necessary to have a material capable of replicating rubber and ensuring strength and flexibility, as well as a long life. Resistance to chemicals and abrasion make TPU suitable for applications in difficult conditions, because it has a good seal in contact with oils, greases and fuel. The high impact resistance offered by the material also makes it a very popular option for smartphone protections and for the housings of other electronic devices. The properties of commercially available TPU therefore include:

excellent resistance to abrasion, cutting, oils and grease;
high performance at both low and high temperatures;
elasticity;
transparency.

Advantages of TPU in Footwear Applications

Thanks to its versatility in formulation according to the mechanical characteristics of the final product, TPU is used in different types of shoe soles: sports, casual, elegant, safety and health. TPU is in fact one of the best performing materials for the production of shoe soles, allowing the creation of products with absolutely outstanding physical and aesthetic qualities. In nature it appears as a transparent compound, but through the addition of masterbatch it can take on any type of color and at the same time offers the opportunity, impossible to replicate with other materials, to give the sole a playful, opaque, metallic, glittery or pearly effect; it also lends itself very well to painting. In summary, the main advantages of using TPU in the production of shoe soles are:

high technical characteristics and aesthetic yield, which make it suitable for the production of any type of footwear;
grip, resistance to abrasive, chemical and atmospheric agents and oils;
dimensional stability;
possibility of customizing hardness;
excellent flexibility;
possibility of applying any type of coloring (glossy, opaque, metallic, glittery, pearly, etc.);
possibility of making varnishes.