Up until now, I have been printing exclusively with PLA filament mainly because my printer came with a large 1 kg roll of the stuff and I’m learning the nuances of my Bibo 2 Touch printer.
PLA filament is fine for starting out, running test prints and printing novelty items. It’s biodegradable, forgiving and easy to work with. The material, however, is brittle making it less desirable for objects that will see a bit of wear and tear.
I have an idea for a new print design that has a flexible, removable cover so I set out to learn about flexible 3D printer filament types and tips for printing with this material. I share my learning in this post. See my earlier post on the more common and some rather exotic filament types here.
Shore Hardness – A Common Way To Characterize Flexible Filament
Before we dive into the various flexible filaments, we need to understand how they are characterized so you know what you are buying and can adjust your print parameters accordingly.
Flexible 3D printer materials are categorized by their Shore hardness so it’s important to know what the number represents for a given material.
The hardness rubber and plastic materials is measured using a Shore durometer which is basically a tool that forces an indenter into the material test specimen. The depth that the indenter penetrates the specimen at a given force is a measure of the material’s hardness.
You will typically see hardness reported as either Shore A or Shore D. For flexible printer filaments, the Shore A hardness is most often reported.
The Shore A durometer is used to measure softer rubbers and uses a truncated cone shaped indenter.
The Shore D durometer is used to measure semi-rigid and rigid plastics and uses an indenter with a cone shaped tip.
The higher the Shore number, the harder the material. Softer printer filaments are generally more difficult to extrude through your printer’s nozzle.
Some common materials and their respective harnesses:
- Rubber Band Shore A 25
- Automobile Tire Tread Shore A 70
- Hard Skateboard Wheels Shore A 98
- Construction Hard Hat Shore D 75
TPE (Thermoplastic Elastomer) Filament
Flexible 3D printer filament is often marketed as TPE filament. TPE, however, is actually not a specific filament material but a class of materials. Thermoplastic elastomers are a class of copolymers that have both thermoplastic and elastic properties. There are six classes of TPE’s
- Styrenic block copolymers, TPS
- Thermoplastic polyolefinelastomers, TPO
- Thermoplastic Vulcanizates, TPV
- Thermoplastic polyurethanes, TPU
- Thermoplastic copolyester, TPC
- Thermoplastic polyamides, TPA
- Not classified thermoplastic elastomers, TPZ
It’s quite likely that filament labeled as ‘TPE’ is one of the six classes of thermoplastic elastomers or some mixture thereof.
There’s really nothing wrong with labeling a flexible filament as TPE it’s just not necessarily telling the consumer the whole story. I would not purchase a TPE filament without also knowing the Shore hardness.
Most of the flexible filaments being offered as TPE have shore A hardness between 80 – 95.
TPU (Thermoplastic Poyurethane) Filament
TPU filament is a very popular flexible filament. It is a bit harder than TPE filament and is also resistant to a number of chemicals and oils such as turpentine, kerosene, gasoline and transmission oil to name a few.
The percent elongation for this material can exceed 600% depending on the manufacturer. For example, NinjaFlex TPU has a 660% percent elongation and Ultimaker TPU 95 has a 580% elongation.
Shore A hardness, like percent elongation, varies by filament manufacturer and ranges from 85 to 95. The harder the material, the lower the percent elongation.
TPU is also generally more easy to print with than TPE though, as will be discussed below, almost all flexible filaments need slightly different printer settings than needed for standard PLA filament.
NinjaTek offers two popular TPU filaments; Cheetah and NinjaFlex.
- Cheetah: 95A hardness; 580% elongation; print speeds similar to PLA
- NinjaFlex: 85A hardness; 660% elongation
Purchase TPU filament including Cheetah and NinjaFlexon Amazon
Purchase TPU including Cheetah and NinjaFlex from Filaments.ca
TPEE a.k.a. TPC (Thermoplastic Polyester Elastomer or Thermoplastic Copolyester) Filament
MakerGeeks, out of Springfield, MO, manufactures their own flexible filament, Maker Flex. With four production extruders they have produced and shipped millions of pounds of 3D printer filament from their 8000 square foot facility.
Maker Flex is made from TPEE which is a polyester-based thermoplastic elastomer and has an amazing Shore hardness of 40 – similar to a rubber band.
The material is FDA compliant and water tight making it appealing for underwater applications. The relative flexibility of printed components can be tailored by adjusting the percent infill of your print job.
I would definitely check this material out, especially if ‘Made in the USA’ is important to you.
- Purchase Maker Flex TPEE from MakerGeeks.com
Flexible PLA (Polylactic Acid) Filament
Flexible PLA is more like plastic and less like rubber. This material won’t stretch like the other flexible filaments described in this post but it will bend unlike regular PLA material.
Being easier to print than TPU, this is a good material if you are just starting out printing flexible materials. It’s a good material for printing things that need to flex but not stretch like belts, or tires.
Shore hardness is around 55 on the D scale.
- Purchase Flexible PLA filaments from Filaments.ca
Printer Settings For Best Results
Printing with flexible filaments can be a slight challenge as the filament material is not readily extruded.
- You’ll want to slow your print speed down to 20- 30 mm/sec and set your extruder retraction to zero.
- Extruder temperatures should also be around 220- 250 C and print bed temperatures around 75 – 85 C.
- Printing with a skirt is recommended to make sure you have filament material in the nozzle before your component build starts.
- Print onto blue painter’s tape or a heated glass bed with glue for best adhesion.
- Increase the extrusion multiplier a bit. The extrusion multiplier determines the amount of filament the printer extrudes. For example, a setting of 1.5 will tell the printer to extrude 50% more material.
NinjaTek has created a great series of videos that walk through many aspects of printing with flexible filament including how guide tubes, extruders and retraction settings can impact your print.
For those of you who have read some of my other posts, you know that I add information on patented technology when applicable.
In the case of flexible filaments, NinjaTek has a pending PCT patent application. A PCT patent application is a single international patent application filed under the Patent Cooperation Treaty (PCT) with a number of countries designated for patent coverage if the application gets approved. It’s like a one-stop-shop for multinational patent coverage.
The NinjaTek patent application, WO 2015/048155 A1 is actually assigned to their parent company, Fenner Inc., Manheim, PA.
The patent application covers a filament having irregularities along its length to reduce the force required to pull the soft filament through the printer’s extruder mechanism. The irregularities are imparted into the filament by inducing die flow instabilities during the filament fabrication (extrusion) process.
Corresponding US patent application, US2015/0084222A1, has been abandoned by the NinjaTek applicants and the international patent application, which is being prosecuted through the European Patent Office, is meeting a bit of resistance so we’ll have to wait and see if the patent grants.
It’s clear that this technology was used by NinjaTek to develop their Cheetah line of TPU filament that can be printed using standard PLA settings.
Summary and Recommendation
There are quite a few options when it comes to flexible 3D printer filament. This stuff can also be tricky to work with especially if you are new to 3D printing.
You won’t be able to simply run flexible filament at the same settings that you run your PLA filament.
To successfully print flexible filament you’ll need to increase your nozzle and bed temperatures and play with print speeds and extrusion multipliers. With the exception of NijanTek’s Cheetah filament, you’ll also have to slow down your print speeds.
Note that Shore hardness varies based on the filament chemistry (TPE, TPU, TPEE) and manufacturer.
You’ll want to know the hardness of the filament you run through your printer as changing to a different filament, even with the same chemical make up, may not give you the same results.
Flexible filament is also rather expensive. Average cost for a 0.5 kg spool runs about $35 so you’ll want to choose carefully.
For my money, I plan on starting out with NinjaTek’s Cheetah TPU filament because it’s engineered to be more user-friendly and still have the rubbery feel.
Click here for my recommendations of the best flexible filaments.
If you want to manage your budget a little tighter, I’d recommend a flexible PLA filament because it will still give you a bendable part and allow you to dial in your printer settings all while being easier on the pocket book.
All the challenges notwithstanding, part of the fun with 3D printing is the trial and error that leads to a successful print so don’t be discouraged from expanding your printing repertoire with flexible filament.
What will you create?
- Purchase Flexible filaments including Cheetah and NinjaFlex on Amazon
- Purchase TPE, TPU including Cheetah and NinjaFlex and flexible PLA filaments from Filaments.ca
- Purchase Maker Flex TPEE from MakerGeeks.com
If you have questions or comments please leave them below. If you have experience printing with flexible filament we’d also like to get your insights as to what has worked well for you.