All about TPU and other thermoplastic elastomers for 3D printing

Polyurethanes are one of the most versatile polymers in use today. They are used in a wide variety of applications to create all manner of consumer and industrial products. Polyurethanes are usually available as thermosets, however, in thermoplastic extrusion 3D printing they are used in the form of thermoplastic polyurethanes or TPU. TPU is part of a family of products referred to as thermoplastic elastomers (TPE).

Generally speaking, thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) that consist of materials with both thermoplastic and elastomeric properties. While most elastomers are thermosets, thermoplastics are in contrast relatively easy to use in manufacturing, for example, by injection molding. Thermoplastic elastomers show advantages typical of both rubbery materials and plastic materials. The benefit of using thermoplastic elastomers is the ability to stretch to moderate elongations and return to their near-original shape creating a longer life and better physical range than other materials. The principal difference between thermoset elastomers and thermoplastic elastomers is the type of cross-linking bond in their structures. In fact, crosslinking is a critical structural factor that imparts high elastic properties.

Thermoplastic polyurethane (TPU) was invented by Lubrizol Engineered Polymers in 1959, and branded ESTANE TPU, while the company was still called BF Goodrich. TPU is a melt-processable thermoplastic elastomer with high durability and flexibility. It can be considered a unique type of plastic bridging the gap between rubbers and plastics. The key to TPU’s versatility is that its hardness can be highly customized. TPU can be as soft as rubber or as hard as rigid plastics. The look and feel of TPU is just as versatile. It can be transparent or colored as well as smooth to the touch or provide grip. Thanks to its thermoplastic nature, it has several benefits such as excellent tensile strength, high elongation at break, and good load-bearing capacity.

One key aspect to keep in mind when considering thermoplastic elastomeric materials is their shore hardness, which measures the flexibility of the material (A) or rigidity (D) according to ISO 868. Shore hardness is a measure of the resistance of a material to the penetration of a needle under a defined spring force. It is determined as a number from 0 to 100 on the scales A or D. The higher the number, the higher the hardness. The letter A is used for flexible types and the letter D for rigid types. Though, the ranges do overlap.

TPU and thermoplastic elastomers filament extrusion

TPU and other elastomeric copolymer filaments are now available from many different suppliers around the world. Spain-based Recreus and USA-based Ninjatek were the first companies to launch products and build the thermoplastic elastomers market in the first half of the 2010s. Recreus’ range of elastomeric filaments are sold under the brand Filaflex. The company is partially owned by Spanish oleochemical giant Repsol which acquired a stake in 2019. Ninjatek is a product line of Fenner Precision Polymers, a Michelin Group company, and as such, it is backed by 100 years of manufacturing, technical and commercial expertise. It now offers 5 different elastomeric filament products (which are sold in Europe by colorFabb).

FDM market leader Stratasys’ offer now includes the FDM TPU 92A, a thermoplastic polyurethane combining flexibility and stretch with abrasion and tear resistance. The material help to eliminate expensive and time-consuming molding or casting methods to produce elastomer parts.

Among the largest third-party providers of TPU filaments for 3D printing, BASF offers a range of elastomeric filaments under the Ultrafuse brand. BASF’s products include filaments based on BASF’s own Elastollan TPU polymer, with flexibility/rigidity ranging from 85A-95A to 45D-64D. Other products include filaments based on rubber-like thermoplastic copolyester (TPE-C) and SEPS. Covestro and DuPont also include a wide selection of elastomeric filament materials. Covestro offers them both directly under the Addigy brand and via the Arnitel line of polymers that was acquired when the company took over DSM’s AM activities. The Arnitel ID2045 is a 50% bio-based thermoplastic copolyester that prints flexible applications twice as fast compared to TPU while also featuring resistance against high temperatures.

DuPont has developed and offers filaments based on the Hytrel brand of elastomeric polymers based on the same pellet materials (see next section). Lubrizol, the original inventor of TPU, offers pellets of its ESTANE material optimized for 3D printing under the ESTANE 3D brand, with several filament manufacturers using them to produce filament products. One particularly relevant initiative was conducted in collaboration with Dutch filament manufacturers colorFabb, leading to a new family of foaming TPU filaments called varioShore TPU. Merely adjusting the temperature and material throughput (speed and layer height) of varioShore TPU can create foam objects with hardness ranging from 90A to 60A.  At temperatures between 200° and 250°C, the material will expand to roughly 1.4 to 1.6 times its original volume. At this temperature, slowing the throughput rate to 60-70% allows a high degree of active foaming to occur, producing very soft printed parts. However, using this same speed setting but lowering the temperature to 190–200°C, the material prints without foaming to create entirely different haptics and harder prints. This innovation even makes it possible to create variable foam densities within a single print.

Common TPU/TPE filament products available commercially for AM

TPU and thermoplastic elastomers for pellet extrusion

Over the past 5 years, several chemical multinational companies have become actively involved in offering TPU and other thermoplastic elastomeric materials for extrusion 3D printing. Covestro and DuPont have launched 3D printing specific grades of TPU and other copolymeric elastomers, available both as filaments and pellets. It should be noted that most elastomer pellets are not used for direct extrusion via LFAM and FGF technologies but rather they are available to plastics extrusion companies for filament production.

DuPont introduced two new Hytrel TPC-ET grades (available in both pellet and filament form), all of which are optimized for 3D printing performance and consistent mechanical properties. Hytrel TPC-ET is described by DuPont as a versatile copolyester material that comes in various hardnesses for a range of different applications. The semi-crystalline material combines sought-after properties, including the flexibility of rubber and the strength and processability of thermoplastics. The material group has low shrinkage properties, as well as heat and chemical resistance, strength and durability. The 3D printing grades of the materials can be translated to injection molding. The new materials are 60 Shore D grades: Hytrel 3D4100PT pellets in natural and Hytrel 3D4100FL filament in black; and 40 Shore D grades: Hytrel 3D4000PT pellets in natural and Hytrel 3D4000FL filament in black.

Covestro’s Addigy (now part of Stratasys) now also offers a complete range of flexible material toolkits for large-scale industrial 3D printing, based on polyurethane as well as thermoplastic polyurethane and polycarbonate raw materials. Users can adjust these material properties to open up flexible new design possibilities for customized products. Addigy offers materials specifically for fused filament fabrication (FFF) as well as granules for FGF processes (see the previous section).

After entering the market by offering a range of TPU powders for 3D printing (see the dedicated section of this chapter), Lubrizol also began offering an expanding portfolio of its ESTANE 3D thermoplastic polyurethane (TPU) for use in fused filament fabrication (FFF) 3D printers. Current applications range from footwear to industrial and healthcare products. Lubrizol’s TPU resins are available as pellets.

Common TPU/TPE pellet products available commercially for AM

TPU and thermoplastic elastomers for PBF

TPU (thermoplastic polyurethane) and generic TPE (thermoplastic elastomer)—with the recent addition of TPA (thermoplastic amide) material powders have opened a wide new range of applications for polymer powder bed fusion processes. Thermoplastic elastomers are particularly well-suited for PBF processes and applications. and Because polymer PBF technologies require no support and thus enable the production of parts with unlimited complexity, TPU and TPE powder bed fusion applications can leverage the material’s inherent flexibility and modify it or enhance by leveraging the part’s geometry.

All thermoplastic elastomers (including TPU) have similar properties to thermoset elastomers (like polyurethane). This means that they are flexible at room temperature but remain dimensionally stable. When the powders are heated, they can be plastically deformed and processed like thermoplastics. Since they are easy to process, they can be used to replace cross-linked elastomers and soft PVC.

The first and most common thermoplastic elastomer used in polymer PBF processes is TPU. There are several different grades of TPU that differ in terms of elasticity (shore hardness, rebound, shape resilience and elongation at break). Most grades show resilience after deformation and a high UV stability, making them suited for many end-use applications, from automotive to consumer industries, such as footwear and sportswear.

In 2019, laser PBF market leader EOS launched EOS TPU 1301 as a step towards 3D printing for mass production applications. TPU materials are widely used in laser PBF for applications that demand elastomeric properties and with easy to process capabilities. To achieve the flexibility and corresponding damping levels needed for different applications, these properties can be adjusted via structural design and the build process parameters used. The EOS TPU 1301 is intended for applications in footwear, lifestyle and automotive, such as cushioning elements, protective gears, and shoe soles.

In 2022. voxeljet began offering on-demand 3D printing services of parts made from thermoplastic polyurethane (TPU) using the High Speed Sintering (HSS) process. The flexible material, characterized by durable elasticity, damping properties and high-impact protection, was developed by Covestro as part of its Addigy range. Covestro’s AM materials business has now been sold to Stratasys, which produces its own thermal PBF systems based on SAF technology. Stratasys SAF systems do not currently support elastoers but that may soon change and it will remain to be seen how this will affect the partnership with voxeljet.

Generic TPE products used in PBF can be compared to vulcanized caoutchouc (rubber) which is characterized by durability and at the same time susceptibility to elastic deformation. But unlike caoutchouc, TPE can be used in additive manufacturing and in many cases is suitable for skin contact applications. Several companies offer TPE materials for SLS, including SLS materials specialists CRP and ALM. Notably, Sinterit was the first company to qualify a TPE powder for a low-cost benchtop SLS system. Evonik now offers a unique elastomeric polymer for SLS, the INFINAM TPC 8008 P, based on an unreinforced polyester-based elastomer.

Another new elastomer developed specifically for PBF 3D printing (it was developed by Evonik for HP MJF technology) is TPA, a thermoplastic amide elastomer. The INFINAM TPA powder is suited for the production of functional high-tech 3D plastic parts—prototypes as well as series products—that call for high extensibility and energy return, such as sports equipment or automobile components. This new ready-to-use powder meets all the processability criteria required for optimized, production-grade parts developed for HP’s Multi Jet Fusion technology, resulting in a reliable experience similar to HP’s branded PA12 polyamide.

Digital Foams

Introduced in 2019, the Digital Foam program by EOS uses highly flexible polymer materials such as TPU and PA 11 to precisely adjust each and every voxel (volume pixel). This way, companies can manufacture products that are more comfortable, safer, lighter, and more customizable. The program accelerates the development and production of 3D printed foams for applications like helmets and soles by combining product design (CAD), materials, part qualification, and additive manufacturing. The program brings these variables together harmoniously enabling companies to produce flexible additively manufactured helmets, customized orthopedic aids and high-performance shoes, as well as many other products, more quickly.

Traditional foams are made from PEBA (polyether block amide) which is also part of the TPE family and can also be 3D printed. This is a plastic developed by Evonik Industries that is very well suited for powder-based 3D printing due to its high elasticity and strength. PEBA, just like TPU, exhibits high elasticity and strength, and also shows excellent chemical resistance in 3D printed form. 3D printing with PEBA is possible with selective laser sintering (SLS) which can produce very precise and stable components, and high-speed sintering (HSS), which also features high precision and high productivity

PEBA can be used to produce shoe soles, midsoles and insoles using 3D printing. The geometric freedom of 3D printing allows for completely free design. This means that the soles can be adapted to an individual foot profile in a material-saving and the function-optimized way by means of topology optimization and lattice structures. Other properties of PEBA in this context are its resistance to permanent loads and the fact that PEBA has a very wide temperature window of -40° to 90°C, in which it does not lose any material properties.
In the automotive industry, PEBA is used primarily for the 3D printing of seals or pressure hoses. Here, too, it benefits from its resistance to chemicals and its good impact strength. Medical technology also benefits in particular from PEBA’s chemical resistance and it is used for precise geometries for connecting plug-in connections, such as in cannulas.

Other foams are 3D printed using photopolymerization technologies. But that’s for another chapter.

*This is an excerpt from VoxelMatters’ Polymer AM 2020-2030 market report. The full 500-page report includes available product price information, yearly material demand and yearly material revenues, with both current data (2020) and a 10-year forecast. The same depth of analysis is included in the report for all main thermoplastic polymer materials: ABS, PLA, Nylon (PA), PAEK (PEEK, PEKK, PEK), PEI (ULTEM), PE, PET, PP, PC, Polysulphones (PSU, PESU, PPSU), ASA, HIPS, PVDF, PVA and more. Additional dedicated analyses are also included for all photocurable and thermoset materials.