From TPE to Soft PLA, flexible 3D printing filaments are widely useful materials to have at the ready. By design, these filaments are basically printable rubber, allowing you to create complex elastic designs that would otherwise be impossible. Flexible filaments come in a variety of colors, chemical makeups, and hardness, giving you the flexibility to apply their various properties.
What are Flexible 3D Printing Filaments?
In general, most rubbers are thermoset; you heat them up, shape them, let them cool, and that shape is final. This isn’t helpful when your 3D printer needs to change the shape of filament from a cylinder to your model. The opposite of thermoset is thermoplastic; you can melt and reshape your material almost indefinitely. By combining plastic polymers with rubber polymers, you get a Thermoplastic Elastomer (TPE). With this same principle, you can combine materials to create Thermoplastic Polyurethane (TPU), Polyester Copolyamide Thermoplastic Elastomer (PCTPE), or Soft PLA (combining PLA and saturating it in a specific chemical to soften it).
These materials are used in many industries from automotive instrument panels, caster wheels, power tools, sporting goods, medical devices, drive belts, footwear, inflatable rafts, and a variety of extruded forms like door trim or as filament. More than 40% of all TPE produced is destined for use somewhere in a vehicle. TPE’s common use in manufacturing makes it an easy transition from large scale manufacturing to 3D printing and rapid prototyping.
If you have printed with PLA filament, you will find it to be hard and brittle; drop it in the wrong way and it shatters. With a flexible material like MatterHackers PRO Series Flex, you can drop it a thousand times over and not break it. PRO Flex can be stretched to 6 times its original length before breaking, and with our normal filament strength testing rig, we ran out of room before it snapped.
Rules to Live by When 3D Printing Flexible Filament:
Rule #1: No retraction
Make sure to turn off retraction for the entirety of you print. Constant retracting and extruding can cause your print to underextrude from having to “refill” the hotend with more filament after each retraction. In some cases, you could even grind a flat spot in the filament preventing you from extruding filament at all. Despite turning off retraction, unless you’re printing an incredibly complex part, you shouldn’t even notice the difference.
Rule #2: Keep it dry
Follow the same procedures used for nylon to dry your flexible filaments: 200°F for six hours in a conventional oven, then turn it off and let the oven cool back to room temperature. You can also use a vacuum oven to dry your filament in a half hour to an hour. Most flexible filaments are hygroscopic to some degree, and will pop and sizzle if you try extruding it wet. These are pockets of water that steam up instantly, leaving voids in your print. These cubes were printed without drying the filament before printing, whereas the bike grip was put in an oven and removed immediately before printing.
Rule #3: Slow it down
With PLA or ABS, you can print FAST. They’re a hard material, so it’s really easy to grip and push the filament through the nozzle. Printing flexibles is like trying to guide one end of a rope by pushing the other. By slowing it down, it’s much less likely to bind up or even wrap around your extruder gear (I’ve had this happen to me, and it was quite the sight). Slower doesn’t mean 10mm/s either, 30mm/s as a maximum speed is a great starting point. Some printers can print faster, others need to go a little slower, but 30mm/s for infill works very well.
Dispelling Some Myths
Bowden vs Direct Drive. Any time printing flexible filaments is mentioned, one of the first comments is how you can’t print flexibles with a bowden-style printer, or that it doesn’t print well. In the past, that comment would be right, but 3D printing and 3D printer manufacturers have made a lot of advances, but the biggest improvement is constraining the filament path. What this means is that from extruder gear to the opening of the nozzle, there is no where for the filament to want to come out of or bind in. It all comes down to, is there room for the filament to squeeze out of after it leaves the extruder gear. If yes, either design a piece to constrain it, or modify your extruder to fill in the gaps.
Taylor wrote a full breakdown and a much more in depth discussion with pictures and more technical knowledge of why exactly bowden vs direct drive isn’t the question you should be asking, so if that interests you, you can read about it here.
Getting the First Layer Right
The first layer is the most important part of any print. There are a few things you need to do to get the first layer to stick well.
- You need the print bed (or print surface) to be level. Use either MatterControl’s mesh leveling, manually calibrate each corner with a piece of paper, or use your printer’s auto-bed leveling.
- You need the extruder to be homed to the correct height from the bed. Even if your bed is level, you need to make sure the nozzle is at the right distance from the bed. Too close and it smears and doesn’t stick, too far and it doesn’t make enough contact and doesn’t stick. You need the goldilocks zone.
- You need a good base material for your flexible filament to adhere to. Blue painter’s tape or a heated glass bed with PVA glue are ideal surfaces for your print bed.
Here is a video from MatterHackers' 3D printing 101 series that will help guide you in the right direction for getting a stellar first layer.
3D Printing on Blue Painters Tape
Blue Tape, or Painter’s Tape, is one of the easiest and fastest ways to get a great print from your flexibles. Here is a quick checklist of things you want to make sure you are doing.
- Make sure each piece of tape lines up edge to edge without any overlap or gaps.
- Don't heat the bed too high when using Blue Tape, it may stick too well to your printed part.
- Replace any tape strips that get damaged when removing parts.
- Replace the tape after 5-10 prints, when parts stop sticking, or when there is a noticeable loss in tape surface texture.
- If your first layer is not sticking - make sure the print head is close enough to make a nice squished line of filament. If that doesn't take care of your problem, you may want to increase the 'first layer temperature' 5 to 10 degrees (start with 5 and increase if necessary).
Blue Tape is not perfect but it is very easy to use and generally gives great results. However, sometimes your parts can pull the tape up off the glass during printing, and you will see some warping when that happens.
3D Printing On Glass With A Heated Bed
When you have a temperature controlled bed, printing directly on glass can be a great option. The recommended bed temperature for flexible filaments vary greatly, from room temperature to 110°C, so follow the recommended bed settings as described in our Filament Comparison Guide.
If you followed the steps to getting your first layer right and your print isn’t sticking, try this:
- It takes more torque to push a flexible filament, so make sure you run the extruder enough before your print starts so there is filament going onto the bed during the entire first layer. Having a skirt at the start of the print is enough to make sure filament is in the hot end by the time it gets started on your part.
- Make sure the extruder temperature is hot enough to properly melt the filament. Otherwise, the plastic may not flow and leave you with sparse layers and infill disconnected from the perimeters.
- Make sure the speeds for your printer aren't too fast. Printing too fast can cause underextrusion and make infill look like a spider web. With flexible filaments, printing faster takes more torque to get through the hot end.
- Turn up the extrusion multiplier a bit more. A great way to get this accurate, is to do an E-step calibration for your flexible filament, because what works for PLA won’t work the same for TPE. What gets you 100mm in PLA might only get you 85mm with TPE, so follow our E-step calibration article to get that set up. Or, once you find the proper E-steps, find the percent difference from the original E-steps, and you have your extrusion multiplier whenever you come back to your flexible, so you aren’t always going through your printer’s firmware. For example, your printer uses 400 E-steps for PLA, and after calibrating you find TPE uses 500 E-steps. 500/400=1.25, so your extrusion multiplier for TPE should be 125% and you can leave your E-steps calibrated to PLA.
When you can get it working well, glass is the absolute best way to print flexible filaments. It makes a great shiny bottom layer and the heated bed ensures that parts stay nice and flat.
Getting The Temperature Right
When working with a new roll of filament for the first time, we generally like to start printing at about 235°C and then adjusting the temperature up or down by 5 degree increments until we get a quality print.
If the temperature is too high
You will see more strings between the separate parts of your print, like cobwebs. If this happens you should try to incrementally lower the temperature by 5 degrees until the extruder is not leaking so much material. Printing flexible filament works much better with retraction turned off, so you may not be able to prevent all strings from occurring, but with the proper temperature, you should have very few issues.
If the temperature is too cold
You will either see that the filament is not sticking to the previous layer and you are getting poor layer adhesion or you will get a part that is not strong and can be pulled apart easily. In either case, you should increase the temperature by 5 degrees and try again until you get good line segments on every layer and have a strong part when done printing.
Note: You may need to experiment with the temperature that will print the best on your printer. Ambient temperature, humidity and the calibration and uniqueness of your printer all play a part in how your prints will turn out.
If you have any comments or contributions, please drop us an email or give us a call. We are always looking for tips, and best practices - and would love to hear from you. Feel free to reach out with any specific questions on the MatterHackers Forum.
Check out our Filament Comparison Guide to get the scoop on all the latest and greatest filaments - Happy Printing!