Thermoplastic polyurethane (TPU) filament has become an increasingly popular material for 3D printing flexible and durable parts. The elastic properties of TPU make it ideal for applications like wearables, phone cases, grips, gaskets, and more. However, printing with TPU can be tricky compared to stiff plastics like PLA and ABS.
This comprehensive guide will walk you through everything you need to know to successfully 3D print with TPU filament, from picking the right TPU material to fine-tuning your slicer settings. Follow these tips and you’ll be printing flexible TPU parts in no time!
What is TPU Filament?
TPU is a type of thermoplastic elastomer that contains both hard and soft polymer segments. The hard segments provide mechanical strength and rigidity, while the soft segments give TPU its flexibility and elasticity. Unlike rubber, TPU can be melted and extruded into a 3D printer filament.
The shore hardness of a TPU filament, measured in units called SHORE A or SHORE D, determines how rigid or flexible the material is. Hardness can range from soft and gummy (20A) to firm and tough (95A). Most TPU used for 3D printing tends to be 85A-95A hardness.
Compared to other flexible 3D printing filaments like TPE or FLEX, TPU offers superior abrasion resistance and better mechanical properties. It’s also more resilient than PLA or ABS. Parts printed with TPU filament exhibit high elasticity as well as tear and puncture resistance.
Benefits of 3D Printing with TPU
There are several key benefits that make TPU a top choice for 3D printing flexible objects:
Durability – TPU prints are very durable due to the material’s shock absorbing properties. This makes it perfect for functional parts that need to withstand impact.
Flexibility – TPU can bend and compress easily without breaking. It provides more flex than any other common 3D printer filament.
Elasticity – TPU will return back to its original shape after being flexed or stretched. This gives it a rubber-like quality.
Wear resistance – TPU holds up very well to abrasion and repeated use without wearing down.
Grip – The inherent tackiness of TPU creates nice grippy surfaces for handles, grips, soles etc.
Chemical resistance – TPU has good resistance to oils, greases, and many common solvents.
Easy post-processing – TPU smoothens easily when sanded or vapor polished due to its thermoplastic nature.
Variety of colors – TPU is available in a rainbow of color options from transparent to opaque.
Applications for TPU 3D Printing
The balance of flexibility, durability, and elasticity make TPU suitable for:
- Wearables – flexible rings, bracelets, watchbands, orthotics
- Shoes – midsoles, insoles, sandal straps
- Cases & Covers – phone cases, camera covers, watch guards
- Grips & Handles – tool handles, grips, sporting equipment
- Gaskets & Seals – waterproof gaskets, dust seals
- Suspension & Dampening – elastic suspensions, shock absorbing bushings
- Prosthetics & Orthotics – comfortable, custom medical devices
- Hobby & Toys – flexible action figures, squishy toys
- Industrial – conveyor belts, oil resistant parts
- Automotive – interior trim, bumpers, door seals
The combination of elasticity, durability, and customizability with 3D printing makes TPU a jack-of-all trades material suitable for products in many industries.
TPU vs Other Flexible Filaments
Here’s how TPU compares to other common flexible 3D printer filaments:
TPE (Thermoplastic Elastomer) – More flexible than TPU but less resistant to abrasion. Difficult adhesion during printing.
FLEX/TPA (Thermoplastic Polyamide) – Also very flexible but limited abrasion resistance. Prone to cracks and fractures over repeated bending.
PVA (Polyvinyl Alcohol) – Dissolves in water. Used for support material in multi-material printing. Not very durable.
NinjaFlex – Brand name TPU with excellent flexibility, elasticity, and layer adhesion. A bit pricier.
TPU95A – Harder TPU with high durability and structural integrity but less flexibility than 85A formulations.
For most applications, TPU provides the best balance of flexibility, durability, and ease of printing. The different brands and shore hardness levels allow dialing in properties as needed.
How to Print TPU Filament
Printing with TPU is more challenging than common filaments like PLA and ABS due to the flexible nature of the material. Here are some key considerations and tips for getting great TPU prints.
Use a Direct Drive Extruder
The flex and compressibility of TPU filament makes it difficult to push through a bowden tube reliably. Using a direct drive extruder is highly recommended for TPU printing.
Direct drive allows precise control over the filament feeding right into the hot end. This prevents the filament from bending and binding in the tube. Most flexible filament printers are designed with direct drive extruders.
For desktop printers with bowden setups, it is possible to print TPU with careful retraction adjustments and slower speeds. But direct drive extrusion is much preferred.
Nozzle Temperature
Print temperatures between 220°C and 250°C are recommended for TPU filament. Higher temperatures in that range produce more flexible prints while lower temperatures are better for rigid, strong parts.
Optimal temperature depends on factors like brand of TPU, shore hardness, print speed, and part design. Printing a temperature tower test with your specific TPU brand will dial in the ideal nozzle temp.
Make sure your hot end can safely reach and maintain these TPU print temperatures. An all metal hot end may be required.
Bed Temperature
Heated beds between 45°C to 60°C provide the right amount of adhesion for TPU. Higher temps can cause excessive sticking and make parts difficult to remove.
If you have trouble getting the first TPU layer to stick, try increasing bed temperature in 5° increments. An adhesion promoter like glue stick or ABS/acetone slurry can also help.
Print Bed Surface
TPU’s flexible and slightly sticky nature means it doesn’t adhere as easily to print surfaces as hard plastics. Using a build plate coating designed for TPU is recommended.
The textured PEI print surface works very well for holding TPU layers in place, even without glue or additives. Other good options are BuildTak, polypropylene, blue painter’s tape, and Kapton tape.
Avoid smooth PEI as TPU will not grip well and is likely to detach during printing. Glass beds usually require an intermediate adhesive layer for adequate adhesion.
Slow Print Speed
Due to the flexible properties of TPU, it does not flow and harden as quickly as rigid materials. Print speeds of 20-50mm/sec are recommended for high quality TPU prints.
Faster speeds can result in messy corners, poor layer adhesion, and inaccuracies in the print. Exact speed will depend on factors like nozzle temperature, filament brand, printer firmware, etc.
Slowing down gives each layer more time to bond as it cools and prevents distortions that can occur with the pliable material. Higher infill speeds can be used but perimeters and top/bottom layers especially benefit from slower speeds.
No Supports
TPU sticks poorly to soluble PVA or breakaway support materials. Overhangs and bridges up to 60° can usually print without drooping so supports are not needed in most cases.
For designs with steep overhangs, a dissolvable support material like HIPS can work if printed at very slow speeds. Otherwise, orient the part to avoid any severe angles requiring supports during printing.
Lower Infill Percentage
Unlike rigid plastics, TPU parts do not need dense infill to maintain shape and structural integrity. Infill as low as 10-20% is often sufficient. Higher infill percentages make TPU parts less flexible.
Low infill also has the benefit of reducing printing time, material use, and weight. For functional TPU parts, 40% infill or less is recommended unless high loads are anticipated.
Increase Number of Perimeters
Since infill can be sparse, adding extra perimeters provides some additional strength and durability. 3-5 perimeters (also called shells or walls) is typical for flexible TPU prints.
This compensates for the low infill and prevents thin spots while adding minimal extra print time. Thicker perimeter walls also reduce pillowing between infill areas on the top layers.
Enable Retraction
Stringing can be an issue when printing TPU due to ooze from the nozzle. Retraction helps minimize this by pulling filament up during travel moves.
The default retraction settings of 1-2mm used for PLA and ABS are often too high for flexible filament. This can cause clogs in the nozzle.
For TPU, shorter retraction between 0.5mm to 1mm is recommended. Retraction speed can also be reduced to 20-40mm/sec to prevent filament grinding.
Slow Initial Layer Speed
Having a slow, solid first layer is key for getting TPU prints to stick to the build platform. Print the initial layer at 10-20mm/sec and 100% infill.
Slow speed gives the first layer time to bond with the bed before the second layer bridges over top. Solid infill prevents gaps that can undermine layer adhesion.
After the first layer, speed and infill can be increased back to normal. This provides a strong foundation for the rest of the print.
Cooling Fans On
Keeping the layers cool is important for proper bonding and preventing flex distortions with TPU. Setting the part cooling fans to 100% is recommended.
The dense first layer adheres better when hot but the remaining layers need ample airflow to set properly. Cooling becomes even more critical at higher print speeds.
Enclosed Build Volume
Because TPU is temperature sensitive an enclosed build chamber helps maintain a consistent ambient environment. Enclosures prevent cooling drafts and hold in heat.
If printing TPU on an open framed printer, using an temporary enclosure made of cardboard or plastic sheeting can help keep temperatures stable and minimize warping.
Best Practices for High Quality TPU Prints
Follow these additional tips and best practices to achieve great print quality with TPU filaments:
- Dry TPU before printing to prevent popping and oozing – 3 hours at 50°C typically sufficient
- Replace nozzle frequently as TPU can erode openings over time – 0.4mm+ nozzle size recommended
- Brush residues off hotend when changing from TPU to avoid charring filament
- Print first layer at 100% infill, remainder at 15-40% infill for optimal flexibility
- Keep overhangs to 45° or less to prevent sagging and maintain dimensional accuracy
- Design interlocking parts, lips, and grooves to assemble objects rather than gluing
- Use fine sandpaper up to 2000 grit to smooth layer lines and improve finish of printed parts
- Vapor polishing works very well on TPU unlike more rigid plastics – gives shine and smoothness
Maintaining Your TPU Printer
To keep your 3D printer running reliably with TPU filament, follow these maintenance practices:
- Clean the feed gear regularly as TPU dust can build up and impede proper gripping
- Lubricate the extruder drive gear to prevent filament shredding
- Check for flattened filament near the gear from tight tension or grinding
- Replace nozzle when erosion causes undersized holes or leaking plastic during printing
- Monitor extruder hobbed bolt for wear – TPU abrasion can quickly dull teeth
- Keep all moving parts properly tightened – motion system, hotend carriage, belts etc.
- Check for loose filament scraps stuck to print head and clean thoroughly
Proper cleaning and component replacement when needed will maximize the uptime of your TPU printing setup.
TPU Post-Processing
One of the benefits of TPU over other flexible filaments is how easy it is to smoothen and finish printed parts. Here are some recommendations for post-print processing and finishing of TPU:
- Lightly sand with fine grit sandpaper up to 2000 to remove layer lines and give a smooth, matte surface texture.
- Vapor polishing works extremely well on TPU unlike more rigid plastics. Acetone fumes give a glossy finish and smooth feel.
- To bond TPU parts together use superglue, two-part epoxy or UV-cured acrylic resin. Cyanoacrylate superglue provides the easiest bonding.
- Fill small seams or gaps with thin superglue before sanding for an invisible finish.
- Paint TPU using flexible paints and primers designed for plastics – spray paint adheres well after proper prep work.
- Mold TPU objects using thermoforming or vacuum forming techniques to create alternate shapes or textures.
With minimal post-processing, 3D printed TPU parts can achieve a smooth, professional finish ready for use. The methods above help take prints to the next level.
Conclusion
From phone cases to cosplay masks, footwear to robot grippers, TPU filament opens up new possibilities for durable, flexible 3D prints. This comprehensive guide on printing with TPU covered everything from material properties and applications to fine-tuning profiles and best practices.
The key takeaways for success are using a direct drive extruder, printing at 220-250°C, enabling retraction and cooling fans, using textured build plates, and slowing things down – print speed, layer height, infill percentage. Keep these tips in mind and you’ll be ready to explore the benefits of TPU 3D printing.
