Thermoplastic polyurethane (TPU) is a class of polyurethane that can be plasticized by heating and dissolved in solvents. Compared with compound‑molded and cast polyurethanes, TPU contains little or no chemical crosslinking in its chemical structure; its molecules are essentially linear, yet they exhibit a certain degree of physical crosslinking.

Now that we know what TPU is, what are its classifications? Depending on the criteria used, TPU can be categorized in many different ways.

For example, based on the soft segment structure, they can be classified into polyester-type, polyether-type, and butadiene-type, which contain ester groups, ether groups, or butenyl groups, respectively. Based on the hard segment structure, they are divided into urethane-type and urethane‑urea-type, obtained using diol chain extenders or diamine chain extenders, respectively.

A common classification divides them into polyester-based and polyether-based types.

Although TPU comes in many varieties, it is classified as a polyurethane based on its molecular structure. So, how is it synthesized?

In bulk polymerization, the process can be further classified into prepolymerization and one-step methods, depending on whether a preliminary reaction is involved: in the prepolymerization method, a diisocyanate is first reacted with a macromolecular diol for a specified period before a chain extender is added to produce TPU; in the one-step method, the macromolecular diol, diisocyanate, and chain extender are mixed and reacted simultaneously to form TPU.

Solution polymerization involves first dissolving a diisocyanate in a solvent, then adding a macromolecular diol to allow the reaction to proceed for a specified period, and finally adding a chain extender to produce TPU.

Melt processing employs techniques commonly used in the plastics industry, such as compounding, calendering, extrusion, blow molding, and molding (including injection, compression, transfer, and centrifugal molding). Solution processing involves dissolving pellets in a solvent or directly polymerizing them in a solvent to form a solution, which is then used for coating, spinning, and other applications.

A material is widely used precisely because it boasts excellent properties, and TPU is no exception.

Like cast polyurethanes (liquid) and blend polyurethanes (solid), TPU exhibits high modulus, high strength, high elongation and elasticity, as well as excellent wear resistance, oil resistance, low-temperature resistance, and aging resistance. Notable advantages of TPU include high tensile strength, large elongation at break, and low permanent compression set after prolonged compression.

Below, we will primarily discuss the mechanical properties of TPU in terms of tensile strength and elongation at break, resilience, and hardness.

① , high tensile strength and high elongation

TPU exhibits excellent tensile strength and elongation. As shown in the data below, polyether-based TPU significantly outperforms PVC plastic and rubber in both tensile strength and elongation.

Furthermore, TPU requires little or no additives during processing, meeting the stringent requirements of the food industry—something that is difficult to achieve with other materials such as PVC and rubber.

② , Resilience is highly sensitive to temperature

The resilience of TPU refers to the degree to which it rapidly returns to its original shape after deformation stress is removed, expressed as recovery energy—the ratio of the work required for deformation to the work recovered upon unloading. It is a function of the elastomer’s dynamic modulus and internal friction, and is highly sensitive to temperature.

The TPU soft segments are PTMG, PCL, and PBA, with relative molecular masses of 1000 and 2000, respectively; the hard segments are MDI-BDO, with hard-segment contents of 48.2% (42.7% for PCL-1250) and 31.7%, synthesized via the prepolymerization method with r0 = 1.05.

As expected, rebound decreases as temperature drops, until a certain point where elasticity increases rapidly again. This temperature is the soft-segment crystallization temperature, which depends on the structure of the macromolecular diol; it is lower for polyether-based TPU than for polyester-based TPU. Below the crystallization temperature, the elastomer becomes very hard and loses its elasticity, so the rebound behavior resembles that of a ball bouncing off a hard metal surface.

③ , with a hardness range of Shore 6 0A--80D

TPU hardness is typically measured using Shore A and Shore D durometers, with Shore A employed for softer TPUs and Shore D for harder TPUs.

Because its hardness can be adjusted by varying the ratio of soft to hard segments, TPU offers a broad hardness range—from Shore 60A to 80D—spanning the hardness levels of both rubber and plastics, while maintaining high elasticity across the entire spectrum.

Currently, the main global producers of TPU raw materials include BASF, Covestro, Lubrizol, Huntsman, Mitsui Chemicals, Takachiho, and others.

As a high-performance elastomer, TPU has a wide range of downstream applications and is extensively used in everyday consumer goods, sporting goods, toys, decorative materials, and other fields. Here are a few examples.

① , shoe materials

TPU is used in footwear primarily for its excellent elasticity and abrasion resistance. Footwear containing TPU offers significantly greater comfort than conventional shoes, making it widely favored in high-end footwear, especially sports and casual shoes.

② , hose

Because TPU hoses are flexible and possess excellent tensile strength, impact resistance, and resistance to high and low temperatures, they are widely used in China as air- and oil‑transfer hoses for aircraft, tanks, automobiles, motorcycles, machine tools, and other types of machinery.

③ , cable

TPU offers tear resistance, abrasion resistance, and flexural durability, while its excellent resistance to high and low temperatures is crucial for cable performance. Consequently, in the Chinese market, TPU is increasingly used in high-end cables—such as control cables and power cables—as a jacket material to protect intricately designed cables.

④ Medical devices

TPU is a safe, stable, and high-quality alternative to PVC that contains no harmful chemicals such as phthalates, which could migrate into blood or other fluids in medical catheters or bags and cause adverse effects. Moreover, specially developed extrusion-grade and injection-molding-grade TPU can be easily used with minimal adjustments to existing PVC equipment.