TPU and Flex Filament: Complete Guide to Flexible Materials

Most hobby 3D printers start with rigid materials like PLA, PETG, or ABS. These plastics are strong and reliable, but they can’t bend or absorb impact without cracking. That’s exactly where TPU and Flex filaments come in. Flexible materials open up an entirely new category of applications: phone cases, gaskets, shoe soles, model car wheels, ergonomic grips, and vibration-dampening parts. But printing flexible filaments comes with its own quirks that often discourage beginners. This guide breaks down what types of flexible materials exist, how they differ by Shore hardness, how to configure them properly in your slicer, and where the most common mistakes that lead to extruder jams happen.

What exactly is Flex filament and how does it relate to TPU?

Flex filament is an umbrella category for 3D printing materials known as thermoplastic elastomers (TPE). Unlike standard plastics, their composition combines a hard plastic component with a rubber component. As a result, the material behaves like a classic thermoplastic when heated, and after cooling it takes on rubber-like properties. So it can be melted, extruded through the printer nozzle, and allowed to solidify back into the desired shape.

TPU, or thermoplastic polyurethane, is the most widespread representative of this category. Technically, TPU is a subtype of TPE, but in the 3D printing world it’s treated as a separate category because it offers significantly better printability than typical softer TPEs. TPU is usually stiffer, which makes it easier to push through the extruder, while still retaining elasticity, abrasion resistance, and chemical resistance to oils and fats.

In practice, the terms Flex and TPU are often used interchangeably. When a manufacturer labels a spool as Flex, it’s usually nothing more than TPU with a specific Shore hardness. The Flex label is more marketing-friendly for newcomers, while TPU is the technically more accurate term preferred by experienced users.

Shore hardness: how to read the number on the spool

The word flexible is pretty vague on its own. To allow individual materials to be compared objectively, manufacturers use the Shore hardness scale, most commonly the A and D series. The lower the number, the softer the material. The A scale covers rubber-like materials, while the D scale covers harder plastics. For hobby 3D printing, the key range falls roughly between 60A and 100A.

In practical terms, Shore 85A is roughly equivalent to a shoe sole or a rubber band. These materials are very soft and quite difficult to print, because the filament tends to twist and bend inside the extruder instead of being pushed into the hot zone. Shore 95A is semi-rigid, comparable to a shopping cart wheel or a car tire. This value has become the standard for 3D printing because it offers an optimal compromise between flexibility and printability. Shore 60D, on the other hand, is semi-rigid like a safety helmet, bending only slightly while maintaining high toughness.

When choosing a filament, it’s useful to first consider the intended application. For a phone case that should have the springiness of a rubber sleeve, TPU 85A or 95A is the better choice. For a functional part that only needs to deform slightly and return to its original shape, the 98A to 60D range is a better fit. Labels like Bambu Lab TPU 95A HF or Prusament TPU 95A clearly signal that this is a versatile medium-hardness material suitable for most projects.

• Shore 60A to 85A: very soft materials, difficult to print on Bowden systems, suitable only for Direct Drive extruders
• Shore 90A to 95A: the gold standard for hobby printing, a compromise between flexibility and printability
• Shore 98A to 60D: semi-rigid materials, easy to print, mild elasticity with high toughness

Types of flexible materials: TPU, TPE, TPC, and Soft PLA

In the hobby segment, beginners most often encounter four main types of flexible materials. Each has its strengths and typical use cases. The choice between them shouldn’t be random, because the differences in processing and final properties are significant.

TPU, or thermoplastic polyurethane, is the most popular flexible filament. It excels in high resistance to abrasion, oils, and fats. It tends to be stiffer than other flexible materials, usually around Shore 95A, which makes extrusion easier. TPE in 3D printing slang refers to softer, more rubbery filaments (often 85A or less). They offer better elasticity but are significantly harder to print due to their softness. TPC, thermoplastic copolyester, is an industrial material with hardness in the 85A to 100A range, resistant to high temperatures, UV radiation, and chemicals. It’s not very common in hobby printing, but it’s used for outdoor applications.

Soft PLA, sometimes called flexible PLA, is a special category. It’s a flexible variant of classic PLA, more flexible than standard PLA but less elastic than TPU. It prints more easily, jams less, and has minimal stringing issues. For truly rubbery applications, however, it lacks sufficient springiness. For most users, TPU 95A remains the most sensible choice when entering the world of flexible materials.

Typical applications for flexible filaments

Moving from rigid to flexible materials means a significant expansion of what a 3D printer can produce. The functional properties of flexible prints open up application categories that are practically impossible with PLA, PETG, or ABS. The 3D printing community has, over the past few years, pushed TPU from an exotic material into the mainstream, thanks specifically to the breadth of its applications.

Among the most common applications are protective cases for phones and tablets, where elasticity absorbs impact energy. Then there are gaskets, O-rings, and seals, where no commercial option exists in the exact dimensions you need. In hobby modeling, TPU is used for RC model tires, vibration-dampening drone components, and rubber chassis. In sports gear, it shows up in protective pads, non-slip pads, and ergonomic grips. Around the house, flexible prints find use as non-slip furniture feet, pads under objects, or repair patches for shoes.

Prototypes and functional tests are a special category. If a designer needs to verify the ergonomics of a future grip or the softness of a specific part, TPU makes it possible to produce a real sample part within hours instead of waiting for injection-molded parts. For small runs where investing in a mold doesn’t make economic sense, TPU is often the only viable path.

• Protective cases for electronics
• Gaskets, O-rings, and seals
• RC model tires and vibration dampers
• Ergonomic grips and handles
• Non-slip feet and pads
• Functional prototypes with rubber-like behavior

Print settings: temperatures, speeds, and retractions

Printing TPU requires different slicer settings than standard PLA. Most branded profiles in OrcaSlicer, Bambu Studio, or PrusaSlicer already include optimized presets for specific materials, so the first step should be downloading the correct profile from the filament manufacturer. If no profile exists for a given material, you can start with the following values and fine-tune them based on results.

Nozzle temperature for TPU 95A usually falls in the 220 to 240°C range. Bambu Lab TPU 95A HF, for example, recommends 220 to 235°C. Bed temperature around 35 to 50°C is enough to ensure adhesion; higher temperatures aren’t needed. Print speed is the biggest enemy of flexible materials: the standard 60 mm/s is practically the ceiling for regular TPU, and you often need to drop to 20 to 40 mm/s so the extruder can push the material through without slipping. HF (High Flow) variants can print at up to double the speed thanks to modified rheology.

Retraction, meaning the pulling back of filament during nozzle travel, should be set to a minimum for TPU. High retractions cause soft filament to crumple inside the extruder and form knots. The recommended value is 0.5 to 2 mm at a low speed of 20 to 30 mm/s. Cooling should be set between 30 and 80 percent depending on the model. A fully open fan helps with small details but reduces interlayer strength. A 0.2 mm layer height is a reasonable starting point; thinner layers improve detail at the cost of significantly longer print times.

• Nozzle: 220 to 240°C (HF variants handle higher flow)
• Bed: 35 to 50°C, PEI or textured surface for adhesion
• Speed: 20 to 40 mm/s for standard TPU, up to 80 mm/s for HF
• Retraction: 0.5 to 2 mm, retraction speed 20 to 30 mm/s
• Cooling: 30 to 80 percent depending on the model

Direct Drive vs Bowden: why extruder type matters

Extruder design plays a critical role with flexible materials. A Direct Drive system places the filament-feeding motor directly above the nozzle, so the filament only travels a few centimeters from the feeder to the hot zone. A Bowden system, by contrast, routes the filament through a long PTFE tube from the motor, which sits on the printer frame, all the way to the print head. The distance can be 30 to 50 cm.

With rigid filaments like PLA, this difference is practically irrelevant. But flexible filaments deform like spaghetti inside a long tube instead of being pushed forward. Softer variants (85A and softer) are practically unusable on Bowden setups, because they compress inside the tube like a spring and the extruder ends up just squishing filament in one spot instead of advancing it. Standard TPU 95A works on Bowden, but it requires significantly slower speeds, shorter and more careful retractions, and often a shorter PTFE tube.

Bambu Lab X1C, P1S, P1P, and H2D use Direct Drive extruders, which lets them handle flexible materials without major issues. Prusa MK4 and Core One also have a Direct Drive Nextruder. If your printer has a Bowden setup (typically older Ender 3, some Anycubic models), it’s worth considering an upgrade to Direct Drive or limiting yourself to stiffer 98A and harder TPU variants. The community reports that combining soft TPE with a Bowden setup leads to frustrating jams in 90 percent of cases.

Hygroscopicity: why TPU needs to stay dry

TPU is strongly hygroscopic, meaning it readily absorbs moisture from the air. A spool left open in a normal office environment for a few days will absorb a significant amount of water, which then affects print results. Wet TPU pops in the nozzle during printing, generates steam, and causes heavy stringing as well as a porous surface. In extreme cases, moisture can cause the plastic to bubble as it exits the nozzle, which manifests as faint crackling audible during the print.

Storage should happen in a sealed container or vacuum bag with a moisture absorber (silica gel). For active use, a drybox that keeps filament in an environment below 15 percent relative humidity is ideal. If the filament is already wet, it needs to be actively dried. Bambu Lab recommends drying TPU 95A at 65°C for 8 hours; Prusa Research lists similar parameters. Specialized dryers like the Sunlu FilaDryer, Polymaker PolyDryer, or SOVOL SH01 allow drying directly during printing.

In practice, with TPU it pays to buy smaller spools (250 or 500 grams) and use them up within a few weeks of opening. A 1 kg spool used occasionally over several months will lose quality long before it’s used up. The investment in a dehydrator pays off after just a few rescued spools, and you can also dry other hygroscopic materials like PETG, ASA, or Nylon.

Common problems and how to solve them

Printing flexible materials brings up specific issues that don’t exist with rigid filaments. Stringing (the formation of webs between prints) is the most common problem. The main culprits are wet filament, nozzle temperature that’s too high, or incorrectly set retraction. The solution is to systematically rule out each cause: first dry the filament, then lower the temperature by 5 to 10°C, and finally fine-tune retraction.

Filament jamming in the extruder shows up as the print suddenly stopping extrusion while the extruder keeps trying to feed. On Direct Drive setups, the cause is almost always print speed that’s too high or aggressive retraction. On Bowden systems, it’s most often a mismatch between material softness and tube length. Poor first-layer adhesion is solved by raising bed temperature by 5°C, lightly cleaning the PEI sheet with isopropyl alcohol, and checking Z-offset.

Poor surface and visible under-extrusion often signal insufficient cooling or nozzle temperature that’s too low. Paradoxically with TPU, slowing the print helps: dropping speed from 40 to 25 mm/s often solves issues with extrusion consistency. If the print comes out too soft or too stiff compared to expectations, the chosen Shore hardness probably doesn’t match the application. In that case, the solution is switching to a different material variant, not further tuning of print parameters.

• Stringing: dry the filament, lower temperature, fine-tune retraction
• Extruder jam: slow down the print, reduce retraction, shorten the Bowden
• Poor adhesion: raise bed temperature, clean the PEI, check Z-offset
• Under-extrusion and surface defects: slow down, check nozzle temperature
• Print hardness doesn’t match: pick a different Shore variant of the material

Comparing the main TPU brands on the market

The TPU filament market has expanded over recent years to include dozens of brands and hundreds of variants. For hobby users, it’s useful to know the main players and how they position themselves. Bambu Lab TPU 95A and 95A HF offer excellent compatibility with Bambu Lab printers thanks to ready-made profiles in Bambu Studio and the AMS system. The HF variant enables significantly higher print speeds, which makes it interesting for production use.

Prusament TPU 95A from Prusa Research came together after lengthy development and emphasizes consistent filament diameter (a key factor for stable extrusion of flexible materials). Polymaker PolyFlex TPU95 is another established choice with a good price-to-quality ratio, available in a wide spectrum of colors. Fillamentum FlexFill TPU comes from Czech production and offers specialized variants (98A, 92A, 85A) for different levels of flexibility. NinjaTek (Cheetah, NinjaFlex) is a traditional American brand of premium flexible materials, frequently used in the professional sector.

For beginners, a sensible start is TPU 95A from the brand recommended for your specific printer. A Bambu Lab X1C or H2D owner will clearly get the smoothest experience with Bambu Lab TPU 95A HF. A Prusa MK4 owner will appreciate Prusament TPU 95A, which Prusa Research has built directly into the slicer profiles. Only after the first successful prints does it make sense to experiment with softer variants or specialized brands for specific applications.

TPU and Flex filaments open up a category of applications inaccessible to standard PLA, PETG, or ABS. The key to successful printing is understanding that flexible materials require a different approach: a Direct Drive extruder, low speed, minimal retractions, and strict control of filament moisture. For starting out, the most sensible choice is TPU 95A from a brand recommended for your printer, ideally with a ready-made slicer profile. Softer variants (85A and below) are best deployed only after mastering the basics. The investment in a filament dryer pays off within a few spools for hygroscopic TPU and significantly improves the consistency of your results.

Affiliate link: TPU and flexible filament is available from eSUN.