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Flexible filaments make it possible to 3D print parts that bend, stretch, compress, and recover their shape. They are commonly used for phone cases, shoe components, protective covers, grips, seals, and cushioning structures.
But printing with flexible filament is not always as straightforward as printing with PLA. A spool may feed normally at first, only for the filament to buckle in the extruder, string between printed features, or produce uneven layers. These problems are often related to how flexible materials respond to pressure, heat, and moisture.
TPU and TPE are two common terms used when choosing flexible filament. Although they are often compared as separate materials, TPU is actually one type of thermoplastic elastomer. Their properties can overlap, but different formulations may behave quite differently during printing and in practical applications.
Understanding these differences makes it easier to choose a suitable material, adjust printer settings, and produce more reliable flexible parts.
TPE stands for thermoplastic elastomer, a broad family of materials that combine rubber-like elasticity with thermoplastic processing characteristics. TPU, or thermoplastic polyurethane, is a specific member of this family.
TPU is widely used in 3D printing because many formulations combine flexibility with tensile strength, tear resistance, and abrasion resistance. Depending on its formulation and hardness, it can be used for anything from flexible covers to functional components exposed to repeated bending and contact.
Other materials marketed as TPE can offer different combinations of softness, elastic recovery, rebound, and printability. Their properties depend on the polymer formulation rather than the TPE name alone.
This distinction matters when comparing commercial filaments. Two materials with the same nominal Shore hardness can have different tensile strengths, elongation at break, rebound resilience, and wear resistance.
For example, eSUN's published technical data for its TPU-95A filament lists a tensile strength of 35 MPa and an elongation at break of at least 800%. These figures describe that product under its specified test method; they should not be treated as standard values for all TPU filaments.
The main challenge is how flexible filament behaves inside the extruder.
In fused filament fabrication (FFF), also known as fused deposition modeling (FDM), drive gears push filament toward a heated nozzle. Rigid materials generally maintain their shape under this pressure. Flexible filament can compress, stretch, or bend instead, particularly when the feeding path has too much clearance or encounters excessive resistance.
If the filament deforms before reaching the hot end, the extruder may continue turning without delivering material consistently. The result can be under-extrusion, gaps between printed lines, or a failed print.
The extruder design therefore matters. Direct-drive systems place the drive gears close to the hot end, reducing the unsupported filament length and generally making flexible materials easier to feed. Bowden systems can also print flexible filament, especially relatively firm grades, but their longer feeding paths may require slower speeds and more careful adjustment.
Flexible materials also behave differently after leaving the nozzle. Depending on the formulation, temperature, and cooling conditions, deposited lines may sag across unsupported gaps before becoming sufficiently solid.
These challenges are manageable. The key is to establish stable feeding first, then adjust printing speed, retraction, temperature, and cooling as needed.
Moisture is a common cause of inconsistent extrusion with flexible filaments.
When wet filament enters the heated nozzle, absorbed water can vaporize and create bubbles in the extruded material. Popping sounds, rough surfaces, visible bubbles, and irregular extrusion can all indicate moisture-related problems. Stringing may also become worse, although it can have several other causes.
TPU and other thermoplastic elastomers can absorb moisture, but their sensitivity varies by formulation. Drying recommendations should therefore come from the manufacturer of the specific filament.
For example, eSUN recommends drying its TPU-95A at 55°C for more than four hours, while its TPE-95A product guidance recommends 60°C for five to seven hours. These are product-specific recommendations, not universal settings for every flexible filament. Always check the instructions for the material you are using.
After drying, store the spool in a sealed container with desiccant. In humid environments or during long prints, feeding from a dry storage box can help maintain more consistent material conditions.
It is best to address moisture before changing retraction or temperature settings. Otherwise, adjustments made to compensate for wet filament may become unsuitable once the material is dry.
Flexible filament needs a feeding path that minimizes unnecessary friction and deformation.
Check that the spool rotates freely and that the filament passes through its guides without sharp bends or obstructions. Drive-gear tension also needs to be appropriate: insufficient tension can cause slipping, while excessive tension can flatten or damage soft filament.
A direct-drive extruder is generally a good starting point for flexible materials because it provides better control over the filament near the hot end.
On a Bowden printer, reducing speed is often helpful. A starting speed of around 20–30 mm/s is a reasonable baseline to test on a printer that struggles with flexible materials, although the ideal speed depends on the filament and machine. Some specially formulated filaments and modern printers can print much faster.
If the extruder clicks, the filament buckles, or material flow becomes intermittent, inspect the feeding path before increasing the temperature or changing multiple slicer settings.
Printing speed affects how quickly the hot end must melt and deliver material. If the printer demands more flow than the system can maintain, extrusion may become inconsistent.
For beginners, a conservative speed of 20–30 mm/s is a useful starting point. Once the filament feeds reliably, increase the speed in small increments and check for gaps, uneven lines, or deterioration in surface quality.
Linear speed is only part of the picture. Nozzle diameter, layer height, line width, and hot-end capacity all influence the required volumetric flow rate.
A filament that prints successfully at 30 mm/s on one machine may work at a substantially higher speed on another. Conversely, a high advertised maximum speed does not guarantee that every model can be printed at that rate without defects.
Retraction pulls filament backward during travel moves to reduce unwanted material flow from the nozzle. With flexible filament, excessive retraction can stretch or deform the material inside the extruder and contribute to jams or inconsistent extrusion.
For a direct-drive printer, a retraction distance of approximately 0.5–1.0 mm is a reasonable initial range to test. Start at the lower end and adjust gradually. Bowden systems may require different settings.
If stringing persists, check moisture and nozzle temperature before increasing retraction aggressively. Some stringing is related to the material's flow behavior and cannot be eliminated simply by pulling the filament farther backward.
The goal is to reduce unwanted material flow while maintaining consistent extrusion when printing resumes.
Flexible filament may sag when printed across unsupported gaps because the deposited material has not yet cooled sufficiently to maintain its shape.
Reducing unsupported spans, adjusting model orientation, and optimizing cooling can improve results. The appropriate fan setting depends on the formulation and the balance between surface quality and layer adhesion.
Supports can be particularly difficult to remove when the support material bonds strongly to the printed part. Adjusting the support-interface gap can make removal easier, although a larger gap may leave a rougher underside.
Where possible, redesign or reorient the model to minimize supports. For complicated geometries, test support settings on a small section before printing the entire part.
Hardness is often the first specification people compare when selecting flexible filament. However, two materials with the same nominal hardness can behave differently under tension, bending, compression, and repeated impact.
One example is eSUN's TPU-95A and TPE-95A filaments. Both are marketed at Shore 95A hardness, but the manufacturer's published comparison shows differences in tensile strength, elongation at break, and rebound resilience.
Source: eSUN's published comparison data for TPU-95A and TPE-95A.
The results illustrate several important differences.
Tensile strength depends on the loading direction. In the reported XY-axis tests, TPU-95A has a tensile strength of 29.63 MPa, compared with 21 MPa for TPE-95A. In the Z direction, however, the reported values are 4.43 MPa and 8 MPa, respectively.
In FFF/FDM printing, the XY and Z directions correspond to different orientations relative to the printed layer structure. A part can therefore behave differently depending on the direction of the applied load. These results are specific to the products and test conditions reported; they should not be generalized to every TPU or TPE formulation.
Elongation at break describes stretching before failure. The XY-axis values exceed 400% for TPU-95A and reach at least 450% for TPE-95A. In the Z direction, the corresponding values are 35.66% and at least 75%.
These measurements indicate how far a test specimen stretches before breaking under specified conditions. They do not, by themselves, establish how well a material returns to its original shape after repeated deformation.
Rebound resilience measures a different property. eSUN reports a rebound resilience of 58% for TPE-95A, while the comparison data do not provide a corresponding value for TPU-95A. Rebound resilience describes energy returned after deformation under a specified test method. It is useful when evaluating materials for cushioning and repeated-impact applications, but it should not be confused with elongation at break or complete shape recovery.
Taken together, these measurements show why no single number can fully characterize a flexible filament. Tensile strength, elongation at break, and rebound resilience describe different aspects of mechanical behavior.
The figures above compare two specific eSUN products. They do not establish that all TPU filaments are stronger than all TPE filaments, or that all TPE materials have higher rebound resilience.
Different applications place different demands on a printed part, so material selection should be based on the properties relevant to its intended use.
For protective covers, grips, and parts exposed to friction, TPU is a common option because many formulations offer a useful combination of flexibility, tear resistance, and abrasion resistance. The required hardness and durability still depend on the application.
For cushioning and repeated deformation, rebound resilience is a useful additional specification. A material with suitable rebound behavior may be worth evaluating for cushioning structures, flexible grips, and components that undergo repeated compression. Compression set and fatigue resistance should also be considered when long-term performance matters.
For parts that undergo substantial stretching, elongation at break provides useful information, but it is not a measure of unlimited elasticity. Tear resistance and recovery after repeated deformation are separate considerations.
For wearable accessories and soft-touch components, hardness, surface texture, and the feel of the finished print all matter. A filament's nominal Shore hardness is useful for initial comparison, but it does not fully predict how a printed part will feel.
For outdoor or chemically demanding applications, check temperature limits, UV resistance, chemical compatibility, and aging performance. These properties vary by formulation and should not be inferred from the material name alone.
Finally, consider printability. A material may have suitable mechanical properties but still be difficult to use on a printer that cannot feed it consistently. A small test print is often the most practical way to verify that the material and machine work well together.
When a flexible print fails, changing several settings simultaneously makes it difficult to identify the cause. A step-by-step approach is more effective.
This sequence helps separate moisture-related defects from feeding problems, flow limitations, and geometry-related issues without making unnecessary changes.
Flexible filament printing becomes more predictable when the material, printer, and part design are considered together. Keeping filament dry, reducing feeding resistance, starting at a conservative speed, and adjusting retraction carefully can resolve many common problems.
Material selection requires the same attention to detail. TPU is a widely used type of thermoplastic elastomer, while other TPE formulations can offer different combinations of hardness, rebound, wear resistance, and printability.
Comparing specific mechanical data provides a clearer picture than relying on material names alone. By understanding what each measurement represents and validating the results on the actual printer, users can choose flexible filaments more confidently and produce parts suited to their intended applications.
But printing with flexible filament is not always as straightforward as printing with PLA. A spool may feed normally at first, only for the filament to buckle in the extruder, string between printed features, or produce uneven layers. These problems are often related to how flexible materials respond to pressure, heat, and moisture.
TPU and TPE are two common terms used when choosing flexible filament. Although they are often compared as separate materials, TPU is actually one type of thermoplastic elastomer. Their properties can overlap, but different formulations may behave quite differently during printing and in practical applications.
Understanding these differences makes it easier to choose a suitable material, adjust printer settings, and produce more reliable flexible parts.
What Are TPU and TPE?
TPE stands for thermoplastic elastomer, a broad family of materials that combine rubber-like elasticity with thermoplastic processing characteristics. TPU, or thermoplastic polyurethane, is a specific member of this family.
TPU is widely used in 3D printing because many formulations combine flexibility with tensile strength, tear resistance, and abrasion resistance. Depending on its formulation and hardness, it can be used for anything from flexible covers to functional components exposed to repeated bending and contact.
Other materials marketed as TPE can offer different combinations of softness, elastic recovery, rebound, and printability. Their properties depend on the polymer formulation rather than the TPE name alone.
This distinction matters when comparing commercial filaments. Two materials with the same nominal Shore hardness can have different tensile strengths, elongation at break, rebound resilience, and wear resistance.
For example, eSUN's published technical data for its TPU-95A filament lists a tensile strength of 35 MPa and an elongation at break of at least 800%. These figures describe that product under its specified test method; they should not be treated as standard values for all TPU filaments.
Why Flexible Filaments Can Be Difficult to Print
The main challenge is how flexible filament behaves inside the extruder.
In fused filament fabrication (FFF), also known as fused deposition modeling (FDM), drive gears push filament toward a heated nozzle. Rigid materials generally maintain their shape under this pressure. Flexible filament can compress, stretch, or bend instead, particularly when the feeding path has too much clearance or encounters excessive resistance.
If the filament deforms before reaching the hot end, the extruder may continue turning without delivering material consistently. The result can be under-extrusion, gaps between printed lines, or a failed print.
The extruder design therefore matters. Direct-drive systems place the drive gears close to the hot end, reducing the unsupported filament length and generally making flexible materials easier to feed. Bowden systems can also print flexible filament, especially relatively firm grades, but their longer feeding paths may require slower speeds and more careful adjustment.
Flexible materials also behave differently after leaving the nozzle. Depending on the formulation, temperature, and cooling conditions, deposited lines may sag across unsupported gaps before becoming sufficiently solid.
These challenges are manageable. The key is to establish stable feeding first, then adjust printing speed, retraction, temperature, and cooling as needed.
Five Tips for Better Flexible Filament Printing
1. Dry the Filament Before Adjusting Settings
Moisture is a common cause of inconsistent extrusion with flexible filaments.
When wet filament enters the heated nozzle, absorbed water can vaporize and create bubbles in the extruded material. Popping sounds, rough surfaces, visible bubbles, and irregular extrusion can all indicate moisture-related problems. Stringing may also become worse, although it can have several other causes.
TPU and other thermoplastic elastomers can absorb moisture, but their sensitivity varies by formulation. Drying recommendations should therefore come from the manufacturer of the specific filament.
For example, eSUN recommends drying its TPU-95A at 55°C for more than four hours, while its TPE-95A product guidance recommends 60°C for five to seven hours. These are product-specific recommendations, not universal settings for every flexible filament. Always check the instructions for the material you are using.
After drying, store the spool in a sealed container with desiccant. In humid environments or during long prints, feeding from a dry storage box can help maintain more consistent material conditions.
It is best to address moisture before changing retraction or temperature settings. Otherwise, adjustments made to compensate for wet filament may become unsuitable once the material is dry.
2. Keep the Feeding Path Smooth
Flexible filament needs a feeding path that minimizes unnecessary friction and deformation.
Check that the spool rotates freely and that the filament passes through its guides without sharp bends or obstructions. Drive-gear tension also needs to be appropriate: insufficient tension can cause slipping, while excessive tension can flatten or damage soft filament.
A direct-drive extruder is generally a good starting point for flexible materials because it provides better control over the filament near the hot end.
On a Bowden printer, reducing speed is often helpful. A starting speed of around 20–30 mm/s is a reasonable baseline to test on a printer that struggles with flexible materials, although the ideal speed depends on the filament and machine. Some specially formulated filaments and modern printers can print much faster.
If the extruder clicks, the filament buckles, or material flow becomes intermittent, inspect the feeding path before increasing the temperature or changing multiple slicer settings.
3. Start Slowly and Increase Speed Gradually
Printing speed affects how quickly the hot end must melt and deliver material. If the printer demands more flow than the system can maintain, extrusion may become inconsistent.
For beginners, a conservative speed of 20–30 mm/s is a useful starting point. Once the filament feeds reliably, increase the speed in small increments and check for gaps, uneven lines, or deterioration in surface quality.
Linear speed is only part of the picture. Nozzle diameter, layer height, line width, and hot-end capacity all influence the required volumetric flow rate.
A filament that prints successfully at 30 mm/s on one machine may work at a substantially higher speed on another. Conversely, a high advertised maximum speed does not guarantee that every model can be printed at that rate without defects.
4. Use Retraction Carefully
Retraction pulls filament backward during travel moves to reduce unwanted material flow from the nozzle. With flexible filament, excessive retraction can stretch or deform the material inside the extruder and contribute to jams or inconsistent extrusion.
For a direct-drive printer, a retraction distance of approximately 0.5–1.0 mm is a reasonable initial range to test. Start at the lower end and adjust gradually. Bowden systems may require different settings.
If stringing persists, check moisture and nozzle temperature before increasing retraction aggressively. Some stringing is related to the material's flow behavior and cannot be eliminated simply by pulling the filament farther backward.
The goal is to reduce unwanted material flow while maintaining consistent extrusion when printing resumes.
5. Plan for Overhangs and Supports
Flexible filament may sag when printed across unsupported gaps because the deposited material has not yet cooled sufficiently to maintain its shape.
Reducing unsupported spans, adjusting model orientation, and optimizing cooling can improve results. The appropriate fan setting depends on the formulation and the balance between surface quality and layer adhesion.
Supports can be particularly difficult to remove when the support material bonds strongly to the printed part. Adjusting the support-interface gap can make removal easier, although a larger gap may leave a rougher underside.
Where possible, redesign or reorient the model to minimize supports. For complicated geometries, test support settings on a small section before printing the entire part.
TPU vs. TPE: What Do the Numbers Tell Us?
Hardness is often the first specification people compare when selecting flexible filament. However, two materials with the same nominal hardness can behave differently under tension, bending, compression, and repeated impact.
One example is eSUN's TPU-95A and TPE-95A filaments. Both are marketed at Shore 95A hardness, but the manufacturer's published comparison shows differences in tensile strength, elongation at break, and rebound resilience.
| Mechanical property | eSUN TPU-95A | eSUN TPE-95A |
|---|---|---|
| Tensile strength, XY axis | 29.63 MPa | 21 MPa |
| Tensile strength, Z axis | 4.43 MPa | 8 MPa |
| Elongation at break, XY axis | >400% | ≥450% |
| Elongation at break, Z axis | 35.66% | ≥75% |
| Rebound resilience | Not reported | 58% |
Source: eSUN's published comparison data for TPU-95A and TPE-95A.
The results illustrate several important differences.
Tensile strength depends on the loading direction. In the reported XY-axis tests, TPU-95A has a tensile strength of 29.63 MPa, compared with 21 MPa for TPE-95A. In the Z direction, however, the reported values are 4.43 MPa and 8 MPa, respectively.
In FFF/FDM printing, the XY and Z directions correspond to different orientations relative to the printed layer structure. A part can therefore behave differently depending on the direction of the applied load. These results are specific to the products and test conditions reported; they should not be generalized to every TPU or TPE formulation.
Elongation at break describes stretching before failure. The XY-axis values exceed 400% for TPU-95A and reach at least 450% for TPE-95A. In the Z direction, the corresponding values are 35.66% and at least 75%.
These measurements indicate how far a test specimen stretches before breaking under specified conditions. They do not, by themselves, establish how well a material returns to its original shape after repeated deformation.
Rebound resilience measures a different property. eSUN reports a rebound resilience of 58% for TPE-95A, while the comparison data do not provide a corresponding value for TPU-95A. Rebound resilience describes energy returned after deformation under a specified test method. It is useful when evaluating materials for cushioning and repeated-impact applications, but it should not be confused with elongation at break or complete shape recovery.
Taken together, these measurements show why no single number can fully characterize a flexible filament. Tensile strength, elongation at break, and rebound resilience describe different aspects of mechanical behavior.
The figures above compare two specific eSUN products. They do not establish that all TPU filaments are stronger than all TPE filaments, or that all TPE materials have higher rebound resilience.
How to Choose the Right Flexible Filament
Different applications place different demands on a printed part, so material selection should be based on the properties relevant to its intended use.
For protective covers, grips, and parts exposed to friction, TPU is a common option because many formulations offer a useful combination of flexibility, tear resistance, and abrasion resistance. The required hardness and durability still depend on the application.
For cushioning and repeated deformation, rebound resilience is a useful additional specification. A material with suitable rebound behavior may be worth evaluating for cushioning structures, flexible grips, and components that undergo repeated compression. Compression set and fatigue resistance should also be considered when long-term performance matters.
For parts that undergo substantial stretching, elongation at break provides useful information, but it is not a measure of unlimited elasticity. Tear resistance and recovery after repeated deformation are separate considerations.
For wearable accessories and soft-touch components, hardness, surface texture, and the feel of the finished print all matter. A filament's nominal Shore hardness is useful for initial comparison, but it does not fully predict how a printed part will feel.
For outdoor or chemically demanding applications, check temperature limits, UV resistance, chemical compatibility, and aging performance. These properties vary by formulation and should not be inferred from the material name alone.
Finally, consider printability. A material may have suitable mechanical properties but still be difficult to use on a printer that cannot feed it consistently. A small test print is often the most practical way to verify that the material and machine work well together.
A Simple Troubleshooting Workflow
When a flexible print fails, changing several settings simultaneously makes it difficult to identify the cause. A step-by-step approach is more effective.
- Check moisture. Look for popping sounds, bubbles, and rough extrusion. Dry the filament according to its manufacturer's recommendations.
- Inspect the feeding path. Check spool rotation, filament guides, drive-gear tension, and possible obstructions.
- Reduce printing speed. Return to a conservative speed and see whether extrusion becomes consistent.
- Review retraction. Reduce excessive distance or speed and test the results.
- Adjust temperature and cooling. Make small changes within the recommended range for the specific filament.
- Review model geometry. Reduce unsupported spans, change part orientation, or refine support settings if sagging and difficult support removal remain problems.
This sequence helps separate moisture-related defects from feeding problems, flow limitations, and geometry-related issues without making unnecessary changes.
Conclusion
Flexible filament printing becomes more predictable when the material, printer, and part design are considered together. Keeping filament dry, reducing feeding resistance, starting at a conservative speed, and adjusting retraction carefully can resolve many common problems.
Material selection requires the same attention to detail. TPU is a widely used type of thermoplastic elastomer, while other TPE formulations can offer different combinations of hardness, rebound, wear resistance, and printability.
Comparing specific mechanical data provides a clearer picture than relying on material names alone. By understanding what each measurement represents and validating the results on the actual printer, users can choose flexible filaments more confidently and produce parts suited to their intended applications.