How to print TPU filament: hardness, feeding and flexible parts

TPU is useful when a rigid part would crack, slip or transfer too much impact. It can make protective covers, feet, bumpers, straps, bellows, simple seals and other parts that need to bend repeatedly.

It is not a universal upgrade from PETG. Flexible filament compresses in the extruder, stretches during movement and can cling strongly to the build surface. The softer the grade, the more the complete feed path and print profile matter.

Start with four decisions:

1. Decide how soft the finished part needs to be.
2. Check whether the printer can guide that grade from spool to nozzle.
3. Use the current profile for the named product.
4. Dry and store the spool according to its manufacturer guidance.

When TPU is the right material

TPU is a strong candidate when the part needs:

• repeated bending without behaving like a rigid hinge;
• impact or vibration damping;
• a compliant grip or non-slip contact surface;
• a protective bumper, sleeve or corner;
• a flexible cable guide, bellows or strain relief;
• a simple gasket where the printed geometry and material have been tested for the actual fluid, pressure and temperature.

TPU is usually the wrong starting point for a bracket, enclosure or mounting plate that must remain rigid and dimensionally stable under load. PETG is often easier for indoor functional parts. ASA is normally the clearer choice for rigid outdoor parts when the selected grade documents the required weather resistance.

TPU is also a material family, not a safety certification. Do not assume that a printed grade is food-safe, skin-safe, medically suitable, fuel-resistant or watertight. Those claims require product documentation and validation of the final printed part.

Choose hardness before colour

Flexible filaments are commonly labelled with Shore hardness values such as 85A, 90A, 95A or 40D. The letter matters: Shore A and Shore D are different scales, so 40D must not be read as 40A.

Within the same product family and scale, a lower hardness normally means a softer filament. Softer filament can produce a more compliant part, but it also buckles and compresses more easily in the feed path.

For a first flexible spool, a well-supported TPU around 95A is often the least demanding place to start. That is not a universal rule: some printers have validated profiles for softer grades, and high-flow formulations can behave differently from conventional TPU.

Do not use an approximate conversion between Shore A and Shore D as a purchasing specification. Compare named products on the same scale and use the manufacturer data for the exact grade.

The printed part is not determined by Shore hardness alone. Its feel also changes with:

• wall count and wall thickness;
• infill type and density;
• model geometry and print orientation;
• the size and direction of the applied load;
• temperature and rate of deformation.

Before buying a softer spool, test whether fewer walls, lower infill or a more compliant geometry gives the required result with a grade the printer can feed reliably.

TPU settings are product-specific

There is no safe universal TPU temperature, speed or drying profile. Current manufacturer examples show substantial differences:

These values are named examples, not a range to average. A soft 30D grade, a 40D grade and a high-flow 95A grade are not interchangeable. Start from the exact spool and printer profile, then change one variable at a time.

Check the complete product page or technical data sheet before drying. A temperature suitable for one TPU can deform another spool, alter additives or exceed the limits of the dryer.

Prepare the filament path

TPU does not transmit pushing force like PLA. If the path between the drive gears and hotend leaves an open gap, the filament can bend sideways instead of entering the nozzle.

A reliable path has:

• a clean nozzle with no partial obstruction;
• drive gears aligned with the filament;
• minimal unsupported space after the gears;
• a smooth route from spool to extruder;
• moderate idler pressure that grips without crushing the filament;
• a freely rotating spool without crossed or snagged turns.

Direct-drive extruders usually make soft TPU easier because the constrained path is short. A Bowden printer can still handle some firmer flexible grades, but the long tube adds compression and delay. Use the printer manufacturer’s compatibility guidance rather than assuming every material labelled TPU will work.

Multi-material feeders add another compatibility layer. Do not route generic TPU through an AMS or similar system unless both the feeder and the exact filament are supported. For example, Bambu lists TPU 95A HF as incompatible with AMS and AMS lite, while its separate 68D TPU for AMS is supported. Compatibility also differs between feeder generations, so check both the exact feeder and the exact filament.

Build surface: adhesion can be too strong

TPU often adheres extremely well. On some smooth PEI or glass surfaces, the risk is not warping but damaging the sheet while removing the part.

Follow the build-surface and filament manufacturer instructions. Depending on the surface, that may mean:

• using a textured sheet approved for TPU;
• applying glue as a release layer, not merely as an adhesion aid;
• avoiding excessive first-layer squish;
• letting the bed cool before removal;
• flexing a removable sheet gently instead of pulling the part vertically.

For example, Prusa’s current Prusament TPU 95A guide recommends its satin, PA Nylon and PP sheets, warns that textured PEI may grip too strongly and requires a separator if smooth PEI is used. Other TPU grades and surfaces may need different preparation.

Test an unfamiliar combination with a small footprint before committing a large part.

A controlled first print

Use the manufacturer profile when one exists. If a validated profile is unavailable, begin conservatively:

1. Select a simple model with few long travels and no difficult supports.
2. Use the nozzle and bed temperatures from the product documentation.
3. Keep acceleration, volumetric flow and print speed modest.
4. Start with little retraction; increase it only after the feed is stable.
5. Use the documented cooling range rather than copying a PLA profile.
6. Watch the first layers for over-compression, under-extrusion or filament buckling.

Do not diagnose every TPU problem with nozzle temperature. Feed resistance, moisture, excess retraction, an unsupported path and an overloaded volumetric flow can all create similar under-extrusion.

Cooling is a balance. More fan can sharpen small details and overhangs, while less fan can improve layer bonding. Stay within the named product range and change it only for a visible reason.

Speed and volumetric flow

Ordinary TPU is commonly slower than rigid filament because the feed system cannot accelerate and retract it as aggressively. The relevant limit is not only the visible travel speed but also the product’s maximum volumetric flow and the ability of the extruder to push it consistently.

High-flow TPU can be much faster, but only with its dedicated profile. A high-speed number from one formulation is not a sensible target for a softer conventional grade.

Retraction

Too much retraction can pull and compress the filament repeatedly until feeding becomes inconsistent. Start with the product or printer profile. If none exists:

• use the shortest practical retraction;
• keep retraction speed conservative;
• reduce unnecessary travels through slicer path planning;
• fix moisture before trying to eliminate every string mechanically.

Some stringing is a more acceptable trade-off than a failed print caused by aggressive retraction.

Drying and dry storage

Many TPU grades are hygroscopic and can absorb enough moisture from the air to affect printing. Sensitivity and drying requirements vary by formulation. Common symptoms include:

• popping or sizzling at the nozzle;
• bubbles or rough patches in the extrusion;
• increased stringing and oozing;
• an inconsistent glossy or matt surface;
• weakened or irregular extrusion.

Dry the exact product at its documented temperature and time. Then keep it sealed with active desiccant. For a long print or a very moisture-sensitive grade, feeding directly from a dry box can prevent the spool from reabsorbing enough moisture to affect the result.

Dry storage does not replace drying. Desiccant is good at slowing moisture uptake and maintaining a dry spool; it may not remove moisture from a saturated filament quickly enough.

See FilamentLab’s filament drying guide for dryer selection, temperature control and storage practice.

Design the part for the behaviour you need

With TPU, slicing and geometry are part of material selection.

To make a part more compliant:

• reduce wall count or wall thickness;
• lower infill density;
• add slots, ribs or thin flexure zones deliberately;
• orient the part so it bends without peeling weak layer interfaces apart.

To make the same material feel firmer:

• add walls;
• use a denser or more supportive infill;
• shorten unsupported flexible sections;
• choose a harder grade within a comparable product family.

Avoid using very dense infill by habit. It adds material and print time and can turn a flexible design into a heavy block without solving the actual load path.

For seals, pressure parts, wear surfaces or safety-related components, test the finished print. Layer lines, seams, porosity and anisotropy mean that a printed TPU part does not automatically inherit every property quoted for an injection-moulded test specimen.

Troubleshooting TPU

The extruder clicks or the filament coils around the gears

Likely causes:

• speed or volumetric flow is too high;
• the nozzle is partially blocked;
• the filament path is not sufficiently constrained;
• idler pressure is excessive;
• the selected grade is too soft for the feeder.

Reduce flow demand, clean the nozzle, inspect the path and return to the product profile. Do not compensate automatically by increasing gear pressure.

The surface is rough and the nozzle pops

Moisture is the first suspect. Dry the spool according to the named product instructions and keep it dry during printing.

The print has heavy stringing

Confirm that the spool is dry before changing retraction. Then reduce nozzle temperature within the approved range and minimise unnecessary travels. If the problem remains, tune retraction in small steps.

Layers are missing after a travel move

Retraction may be too long or too fast, or the filament may be compressed in a Bowden path. Reduce retraction and verify that the extruder resumes a consistent flow.

The part is too soft

Add walls, change the geometry or select a harder grade. Infill alone may not provide the required stiffness.

The part is difficult to remove

Do not force it off a delicate surface. Let the bed cool and follow the sheet maker’s release method. For the next print, use the approved separator or a more suitable build surface.

TPU, PETG or ASA?

Use the required behaviour to decide:

Read the PETG guide or ASA guide when flexibility is not the primary requirement.

Frequently asked questions

Is 95A TPU easy to print?

It is often easier to feed than softer flexible grades, but 95A alone does not guarantee an easy print. The formulation, feeder, profile and model still matter. Use the exact product profile and confirm the feed path is supported.

Can a Bowden printer use TPU?

Some can print firmer grades reliably at conservative speeds. Very soft TPU is more demanding because the long filament path stores compression and gives the material more room to buckle.

Does TPU always need drying?

Use the spool manufacturer’s instructions. Many TPU products require or benefit from drying, but the correct temperature and time vary substantially.

Should TPU be printed in an enclosure?

Many common TPU grades do not need a heated enclosure. The product documentation and printer airflow still control the answer; an enclosure is not a substitute for correct cooling or a dry spool.

Can TPU go through an automatic material system?

Only when the exact feeder and TPU grade are documented as compatible. Generic TPU may require an external spool or bypass even when a special “TPU for AMS” product is supported.

A practical decision

Choose TPU because the part needs controlled flexibility, damping or grip, not because it sounds more technical than PETG. Select the hardness and formulation your printer can feed, use the named profile, keep the spool dry and tune the geometry before chasing a softer material.

When that behaviour matches the job, continue with the TPU filament collection. If the part should remain rigid, compare PETG and ASA instead.