Flexible Filament

When people think of 3D printing they think of parts or objects made using rigid (stiff) materials. It’s natural since we associate the word ‘plastic’ with rigid objects like water bottle, drinking cups, spoons and mice (the computer kind) to name a few. But 3D printing filaments also comes in flexible varieties called TPU. TPU stands for Thermoplastic Polyurethane. It is a material that is both flexible and strong. Think of TPU like a hard rubber – strong enough to hold its shape but flexible enough to bend and deform without breaking.

Why Use TPU

TPU is used when the part needs to flex or otherwise be deformed. A good example would be a one-piece hinge. If the hinge were made of a hard material the flex point on the hinge would eventually break, but since TPU is elastic the flex point would bend and stretch as needed. The amount of flex can be controlled by adjusting wall thickness (aka perimeters), amount and type of infill and layer thickness. Thinner walls, thinner layers and less infill creates a part that is more flexible than one with thicker elements.

3D Printing Considerations

If you’ve decided that TPU is the material to use for your project, then you should be aware of the issues associated with printing TPU. When printing, TPU is very sticky! If you print TPU using the same first layer offset as you use for PLA, PETG or ABS (for example) you’ll find that your TPU part is stuck very firmly to your print surface. In fact, it may be so firmly stuck that the only way to remove it is to freeze your print bed, and even that may not work. To avoid this problem its best to adjust your first layer height so that your nozzle is further away from the print bed (increase your first layer height). Exactly how much you’ll need to increase it will depend on your particular setup, but as reference we usually increase first layer height by 0.25 millimeters. You may want to use that as a starting point to tune your first layer offset as you may need more or less. With TPU it’s better to start too high and slowly decrease the height than the other way around. If you start too low you’ll end up with a print bed that has TPU stuck to it that you’ll never get off. You’ll also want to slow down your print speed to get the best result.

Some printers have a feature to automatically determine the first layer offset. If your printer has this feature, or if you have found that simply adjusting the first layer offset isn’t sufficient, you may want to try using a release agent like glue stick. Many people think of glue stick as just the opposite – something you use to make your print stick to the bed better. But because glue stick forms a slightly gooey layer between the part and the print bed it actually helps as a release agent. Since the part is laying on top of the gooey glue stick and isn’t stuck directly to the print bed, removal is easier than printing directly on the bed.

For more information on printing with TPU look here.