Choosing TPU for 3D Printing: Shore Hardness, Flexibility and Pre-Print Checks

If you want to print a flexible protective case or a model that springs back after being pressed, TPU is a useful flexible material to understand. Start by deciding how the part needs to deform, then check the filament’s Shore hardness, printer compatibility and material data sheet. Wall thickness, infill and shape also affect how soft the finished part feels.

TPU stands for thermoplastic polyurethane. It is a type of thermoplastic elastomer (TPE), and TPU filament for FDM/FFF lets desktop printers produce elastic parts. Choose a specific brand and grade: two spools labelled “TPU” may have different feeding and printing requirements.

How to read Shore A and Shore D

Shore hardness measures a material’s resistance to indentation by a test probe. Shore A is commonly used for softer rubbers and elastic materials, while Shore D is commonly used for harder materials. Within the same scale, a higher number generally indicates a harder material.

A and D use different measurement conditions, so always read the number together with its letter. For example, 90A and 90D represent different hardness levels. You cannot arrange 55A, 95A, 64D and 77D on one evenly spaced scale. For comparisons across scales, check the material’s test method and manufacturer’s data. Smooth-On’s guide to Shore hardness explains the ranges and overlap of the two scales.

How soft will a 95A TPU print feel?

95A describes the material’s hardness; the feel of a printed part also depends on its structure. Thin walls bend more easily, while thicker walls and more infill provide more support. A thin sheet and a thick solid block made from the same spool of TPU can feel very different.

For example, Prusament’s TPU 95A material guide describes flexibility in thin layers and toughness in thicker layers. When trying a material for the first time, print a thin sheet and a small sample with a wall thickness close to your final part. These make it easier to judge than the hardness number alone.

Define the use, then check the material data sheet

Write down how the part will be used: does it need to bend, compress or hold its shape? What temperatures and contact conditions will it face? Then match those questions to the data sheet.

What you need to know	What to check when choosing a material	How to test a sample
Will it bend to the required angle?	Shore hardness, elongation and grade-specific data	Test bending with a similar thickness and shape to the final part
Will it recover after being pressed?	Resilience, compression set and test conditions	Record dimensions before and after compression, and how the sample recovers
Will the fit be too loose or too tight?	Actual printed dimensions, wall thickness and fit clearance	Print the joint area and test assembly and removal
Will it withstand its intended environment?	Temperature, abrasion resistance and data on substances it will contact	Arrange suitable tests for the expected environment

These samples help refine everyday models and prototypes. For parts used in medical applications, food contact, electrical insulation or safety protection, material selection and validation need to follow the certification, material documentation and product-testing requirements for that use.

Checks before printing TPU

1. Check the printer and filament path

Check which flexible filaments your printer supports and the grade you plan to use. Pay particular attention to compatibility with the extruder, tubes and automatic feeding devices. Flexible filament may buckle when pushed; a longer path or higher resistance can make feeding more difficult.

Prusa’s flexible-material guide lists common problems such as filament winding around gears, stringing and difficult support removal. Follow your printer’s loading instructions first and watch whether the filament moves smoothly.

2. Dry and store the filament as its manufacturer specifies

Check the recommended drying temperature, duration and storage method. Moisture behaviour varies between TPU grades. Prusament’s TPU 95A guide says pre-drying is usually unnecessary, but moisture problems caused by poor storage need to be addressed according to its instructions.

If you hear popping or see bubbles or an unusual surface during printing, check the filament’s condition first, then test the result after drying. Record the grade and treatment method so you can repeat the process.

3. Start with a matching material profile

Use the manufacturer’s profile for that grade and printer where available, and check the nozzle, temperature, flow and speed. Start with matching retraction settings too, then test gradually. A large increase in retraction may make flexible filament harder to feed consistently.

Check the build-plate preparation as well. Some TPU grades bond strongly to particular surfaces, and the manufacturer may require a separation layer. Follow the plate and filament instructions when removing the print to protect the surface.

4. Print a sample and change one setting at a time

Choose a sample that reflects the final part, such as a thin wall, joint or section that needs to bend. Keep the original profile and record each change, the surface result and how the part feels during assembly and removal. Changing one setting at a time makes it easier to see what works.

What to adjust if the part feels too stiff or too soft

If the sample is too stiff, test thinner walls or less infill. If it collapses too easily, try increasing local wall thickness or adding supporting structure. Keep the material and other conditions the same while comparing samples, and refine the shape gradually.

Consider the bending direction and print orientation too. Where will the part be pulled in use? Will the joint be loaded repeatedly? Reducing overhangs that need supports can lower the chance of surface damage during support removal. Refine the clearance after a test fit so that thin walls are not stretched excessively just to make the part fit.

Common problems: stringing, uneven feeding and inaccurate dimensions

• Heavy stringing: Check the filament’s condition and profile first, then test temperature, travel and retraction settings. You can also read the 3D printing stringing troubleshooting guide.

• Intermittent extrusion or filament winding around gears: Stop the print. Unload the filament and check the path according to your printer’s instructions, then check feeding resistance and speed.

• Joints that are too tight or too loose: Confirm that feeding is stable before comparing sample dimensions. Apply measuring tools gently to avoid compressing the flexible part.

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