Printing Flexible Filaments

TPU- Thermoplastic Polyurethane

I recently have interest in printing using flexible filaments. I want to print a flexible cover for a Trace Together token. Originally, I thought the only material that’s stretchy and flexible is rubber. But doesn’t rubber burn when heated! From readings, now I know that there’s this material called TPU (Thermoplastic Polyurethane). TPU is often regarded as a mixture of rubber and plastic- it has the elasticity and flexibility of rubber but the strength & durability of plastic. TPU is currently the most common flexible material in FDM 3D printing. The other material is TPE (Thermoplastic Elastomer) but is not nearly as popular choice yet.

TPU is actually very widely used amongst the everyday products we use. Wheel toys is a good example. Another example is the flexible and soft mobile phone back cover. But you may find that one back cover is more flexible or rigid than other and that is because different ‘hardness’ of ‘softness’ TPU characteristics. This characteristic is often called the ‘Shore Hardness’. The lower the number, the softer it is- as you can see from the chart below. The most common TPU filaments that are available for 3D printing are ones with shore hardness 85 and 95.

TPU Shore Hardness (https://3devo.com/blog/tpu-3d-printing-polymer-twist/)

Printing TPU 95

I decided to try to print out in TPU using my Ender 3 v2. TPU 95 seems the easiest to print. The other challenge that remains is the recommendation to use printer with Direct Drive rather than Bowden Extruder to feed the filament into the hot-end of the print head. Ender 3 v2 employs Bowden Extruder.

In Bowden Extruder, the stepper motor clip is attached to the frame and is stationary. The filament would enter from this clip, and need to travel to the hot end of the extruder via PTFE tubing. This is where the trouble may arise that the filament may not make that journey successfully into the hot end. But the only want to know for sure is to try it myself to print TPU with my Ender 3 v2.

Purchasing TPU Flexible Filament in Singapore

TPU is widely available in Singapore through popular online shopping platforms. However one of the challenges I faced was that the shore hardness information is often not available. So you need to do a bit of asking. If this is your first time printing in TPU, I suggest to stick to TPU 95, which is the easier model to print. Only after you are confident how to handle TPU 95 and you know that your printer can print TPU 95, then I suggest you can move to softer TPU like TPU 85. I purchased Sunlu brand TPU 95 for this project.

Printing TPU 95 with Ender 3 v2

Yes! It is possible printing flexible filaments with Ender 3 v2. I have done it successfully to print TPU 95. It took me 2 tries to get the correct settings, which I will share below.

First, feed the filament normally as you would with PLA. The filament is a bit softer so you would need to push it through the tube a bit slowly all the way to the hot end.

Then set the settings on Cura to print in TPU. The most important settings are temperature and print speed. Below is what I used:

Printing temperature: 210 deg C.
Build plate temperature: 55 deg C.
First layer temperature: 55 deg C.
Print speed: 20 mm/s.
*ps: I use Infill density of 40% because I am printing with transparent TPU. At lower density the printout does not turn out nice as it would show the infill pattern. I find 40% would offer optimal result.
Other printer or other filament brand might use slightly different settings.

If this is your first time printing flexible TPU filaments and just cross over from other type of filament, I suggest you run a test print to ensure your printer can extrude TPU correctly. Once test print is completed, you can print the actual design more confidently. Here is what I printed: