Flexible 3D printing filament can be used to print everything from grippy feet for furniture to springy shoes that absorb shocks. Though there are a lot of reasons you might want to try printing with TPU, you should be aware of the challenges it poses before you try.
Flexible filaments like TPU can be challenging to print
Thermoplastic polyurethane (TPU) is the most common flexible 3D printer filament, and it’s considered to be the easiest flexible material to print with. It’s commonly chosen for its impact resistance, flexibility, and color choice. It tends to have good bed adhesion, which is another plus.
Despite being versatile, TPU’s flexible nature can be a source of frustration. In 3D printers that don’t have the filament motor in the print head, TPU can buckle and struggle to make it through the PTFE Bowden tube, causing jams and failed prints.
It’s also a highly hygroscopic filament, which means it absorbs moisture in the air to a greater degree than PLA or PETG. This can lead to stringing, poor surface finish, bubbling, and failed prints if you don’t dry it out adequately and store it properly before printing.
TPU is just one of many, with others like thermoplastic elastomer (TPE) being even more flexible, polyether block amide (PEBA) offering more bounce, and flexible PLA using the same polylactic acid as standard PLA (but with extra ingredients that take away the material’s brittle nature).
Don’t get too excited about that last one. Just like any other flexible filament, flexible PLA is subject to the same challenges on account of its rubbery qualities.
You need to match your filament with your extruder (and accessories)
Tim Brookes / How-To Geek
Flexible filaments like TPU are measured using the Shore hardness scale, with ratings consisting of a letter (in this case, A) and a number. The lower the number, the softer and more flexible the filament. The softer and more flexible the filament, the harder it is to print using a traditional Bowden tube setup.
Bambu Lab recommends printing with a hardness rating of 85A or higher “for stable printing.” The company also sells a TPU Feed Assist Module ($50) for its H2, P2, P1, and X series printers to improve finish by adding “an active, consistent push to the filament.”
If your printer has a direct drive extruder, where the filament motor is mounted directly on the print head, you should have far fewer problems printing with flexible filaments. Unfortunately, most consumer-grade 3D printers use a PTFE Bowden tube setup to help guide the filament to the print head.
If you don’t go the direct drive route, you’re probably better off sticking to the TPU manufactured or stocked by your printer brand. Bambu Lab sells TPU for AMS, a filament designed specifically for use in the company’s multi-material system, with a somewhat disappointing Shore hardness rating of 68D.
Flexible filaments require slower print times
If you’re trying to print TPU in a standard Bowden tube setup, be prepared to endure slow printing times to prevent the filament from buckling and jamming. Speeds of around 30mm/s are often recommended. Even though it’s possible to print faster, you’re risking a jam and wasted filament if you do so.
Even when you’re using a direct drive extruder or TPU helper add-on, you’re going to be printing slower with TPU than you would with PLA or PETG. Expect something around 60mm/s at the high end.
The softer the material, the slower you’ll want to print to give yourself the best chances of success. For example, Snapmaker recommends no more than 40mm/s for 90A and 95A TPU.
Flexible filament can be expensive
TPU might be commonly available, but it’s also expensive compared with alternatives like PLA. For example, Bambu Lab’s TPU for AMS costs $39 for a 1kg spool, while the company’s 85A TPU will set you back $45 for the same amount. Ninjaflex 85A TPU, widely considered to be one of the highest quality flexible filaments, costs just over $100 for a 1kg spool.
Even flexible PLA, which is usually cheaper than TPU, can cost roughly double what you’d spend on basic PLA.
The reality is that it’s probably cheaper to buy many of the everyday items you might otherwise print with TPU. This isn’t to say that the material doesn’t have its uses, but rather that it feels less versatile and prone to experimentation in the way that PLA is. This doesn’t really apply if you’re designing your own prints from scratch with TPU in mind.
Flexible filaments can be a bit too sticky
Poor bed adhesion is usually seen as a bad thing, but TPU doesn’t suffer from this issue in the same way that ABS and PETG can. In fact, under ideal bed conditions of around 30-60ºC, TPU can stick a little too well.
A heated bed is recommended to prevent the print from warping and to provide a solid first layer, but you might want to break out the glue stick in order to make the print easier to remove (especially when printing on glass or other smooth plates).
If you want a 3D printer for TPU, consider the new Bambu Lab X2D, which includes a direct drive motor and a secondary nozzle that’s perfect for printing supports from PLA in less time than it takes a single-nozzle printer to change filament.
Stephan is the sports journalist for the Maple Grove Report.
