Types of Flexible Filament: TPU
While there are several flexible 3D printing materials on the market, the two major types of flexible filament are Thermoplastic Polyurethane (TPU) and Thermoplastic Elastomer (TPE). Both of these are made from thermoplastic elastomers which are derived from a blend of hard plastic and soft rubber. While terminology is often mixed, thermoplastic polyurethane (TPU) is the most commonly used flexible material within the 3D printing industry.
How is Flexible Filament Measured?
What sets many flexible filaments apart is the degree of flexibility they offer. Most materials are measured on a “Shore Hardness/Durometer” scale which is the measure of the resistance a material has to indentation.
Typically the durometer of materials like flexible 3D filament is denoted as being on either the Shore A or Shore D scale. Softer materials such as flexible filament for 3D printing are measured on the Shore A scale, while Shore D is reserved for harder rubbers.
Flexible Filament for 3D Printing
Flexible Thermoplastic Urethanes (TPU) filaments within the 3D printing industry range between Shore A 60 – 90 and are classified as being ultra-flexible to semi-flexible. Depending on the application, there is a flexible filament that provides the necessary properties to meet the demands of its users.
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Semi-Flexible TPU Filament
The most rigid flexible filament is a semi-flexible TPU with a Shore A Durometer of 90 (90A). This material is ideal as an introductory to printing flexible filament because its shortcomings are lessened by its degree of hardness. A Shore A 90 material is classified as a hard material and depending on the infill, it can be printed in a manner that is rigid while maintaining flexible properties. It is an ideal material when you need a degree of flexibility but still need structural stability and can be successfully printed on a Bowden-type extruder.
Flexible TPU Filament
The most common flexible filament is a Flexible TPU with a Shore A Durometer of 85 (85A), which is comparable to other flexible filaments offered on the market, such as NinjaFlex. A Shore A 85 material is classified as a medium-hard material but it is actually quite flexible and offers a wide variety of flexibility depending on infill. While an 85A flexible filament can be printed on a Bowden extruder, it takes a well-optimized setup due to its steep learning curve. It is ideal for items such as gaskets, grippers, hinges or RC tires and components.
Ultra-Flexible TPU Filament
The most flexible filament is an Ultra-Flexible TPU with a Shore A Durometer of 60 (600A). A Shore A 60 material is classified as medium-soft material but it is extremely flexible, even with a high degree of infill. It is highly recommended to use a well setup direct drive extruder or a Flexion Extruder from Diabase Engineering to even print with it. An ideal application is overprinted parts (such as rigid components with incorporated gaskets) or soft robots.