3D Printing with Flexible Filament A Beginner's Guide to Flexible Filament
This article explains the most common types of flexible filament—TPEs. The characteristics of TPU, TPC, TPA, and soft PLA are described to facilitate your foray into these flexible materials.
3D printing is an increasingly common technology for both consumer and industrial applications. This has facilitated a growing interest in producing customized solutions for a variety of products, such as clothing and prosthetics. These easily customizable, wearable objects typically require sturdy but flexible materials that cannot be produced with traditional thermoplastics. For these applications, rubber is the ideal choice. However, rubber cannot be 3D printed (yet!), so manufacturers have developed alternative materials that can serve a similar function to rubber for 3D printing applications.
Thermoplastics and elastomers are effective and widely used flexible materials, and these have been combined to form a new class of 3D printing material called thermoplastic elastomers (TPEs). TPEs exhibit excellent compression to counter loads, which increases their durability without sacrificing flexibility. Although they can be difficult to use, the results make it worth practicing with these special materials. In this article, we cover the most common TPEs as well as another type of flexible filament called soft PLA.
TPEs are polymers that have similar elastic characteristics to cross-linked rubbers. Elasticity is dependent on the type of TPE and its chemical structure. Beyond exhibiting good elasticity, TPEs also possess the processing advantages of thermoplastics, which make them suitable for 3D printing.
There is a huge variety of TPE filaments on the market, so beginner makers may be overwhelmed by the options available. While not all varieties of flexible 3D printing materials are marketed as TPEs, most will belong to one of the categories presented in this article. As always, it is important to research each filament you are planning to buy to ensure that it meets your specific printing needs. We cover the essential characteristics of each material to make this process easier.
Why work with TPE?
- High fatigue resistance
- Excellent electrical properties
- Good vibration damping and shock absorption
- High impact strength
- High chemical and weathering resistance
- High tear and abrasion resistance
- High temperature resistance (−30 to 140 °C)
- Excellent for wearable prints
3D printer settings for TPE prints
To ensure that the final print maintains flexibility and structural integrity, it is crucial that your printer settings are properly tuned. The following general recommendations should be followed but be sure to check the manufacturer instructions for your specific material for details.
- Extruder temperature: 210–260 °C
- Bed temperature: Up to 110 °C or unheated
- Print speed: 5–30 mm/s
- Bed adhesion: Additional adhesive (e.g., glue or spray) is recommended
- Extruder system: Direct drive recommended
- Cooling fan: Part cooling fan recommended
Some materials have highly variable printing needs, particularly for bed temperature and print speed. It is always recommended to perform a test print after tuning the manufacturer’s settings. We also recommend starting with a lower print speed and slowing increasing it if the test print does not set properly.
TPE printing problems
TPEs are a bit more challenging than normal PLA filaments for beginner print makers. Because they are much softer than other filaments, they can be extruded poorly, which can lead to uneven layer setting or gaps.
TPEs are also hygroscopic—meaning that they absorb moisture from the air. If the material is not stored properly, the filament can cause problems when heated owing to this stored moisture. Whenever you are working with a material that is water-sensitive, it is highly recommended to store it in an airtight container in a dry area.
As a highly flexible material, TPEs are very sensitive to rapid extruder movements and high print speeds. The filament can buckle or extrude poorly at higher speeds.
Types of TPE materials
TPEs are classified according to their chemical structure and Shore hardness values, which is a standard material hardness metric.
There are three primary printable grades of TPE materials:
- Thermoplastic polyurethane (TPU)
- Thermoplastic co-polyester (TPC)
- Thermoplastic polyamide (TPA)
Thermoplastic polyurethane (TPU) is the most common TPE material for 3D printing. Compared to other flexible filaments, it is more rigid, which facilitates easy extrusion without requiring too much fine-tuning. It also exhibits good strength and durability for a flexible material.
- Elasticity range of 600–700%
- Shore hardness value between 60A and 55D (moderate flexibility to semi-rigidity)
- Easily printable
- Highly resistant to oil
- Durable with high abrasion resistance
TPU is prone to stringing at high temperatures. Also, TPU exhibits low UV light resistance, so filaments and prints need to be stored carefully.
Thermoplastic copolyester (TPC) materials are copolyether esters with random-length sequences of alternating long-chain or short-chain glycols. These materials are characterized by hard and soft segments: the hard segments are short-chain ester units, while the soft segments are usually aliphatic polyethers or polyester glycols. TPC is typically considered to be an engineering-grade material, making it somewhat uncommon for 3D printing hobbyists. However, people who use their 3D printer for their small business or who are serious about 3D printing custom items might benefit from using this material.
- Elasticity range of 350–530%
- Low density
- Shore hardness value between 40 and 72D
- High chemical resistance
- Excellent thermal stability
- High temperature resistance
TPC exhibits lower elongation and poorer flexibility than other TPE materials.
Thermoplastic polyamide (TPA) is a chemical co-polymer of TPE and flexible nylon that is smooth and highly flexible.
- Elasticity range of 370–497%
- Shore hardness value between 75 and 63A
- High durability
- Easily printable
- High heat resistance
- Good flexibility
- Good layer adhesion
TPAs are more prone to high moisture absorption than similar materials, requiring special storage care. Print warping is somewhat common, so makers are recommended to carefully tune their print settings as this material is less forgiving than similar materials.
Soft PLA includes any PLA blends that are more flexible than traditional 3D printing filaments. Many makers consider soft PLA to be similar to a tough rubber-type material.
It is stronger and more durable than other flexible materials. It does not require as nuanced of setting tuning as TPEs and can be treated similar to standard PLA, only requiring slower print speeds and higher bed temperature.
Soft PLA characteristics
- Shore hardness value between 90 and 92A
- High strength
- High durability
Soft PLA limitations
Owing to its softness compared to traditional PLA, some makers have problems loading the filament properly. It is recommended that, when working with any flexible filament, small test prints are performed first to become accustomed to the specific requirements of each filament type.
While working with new filament types can be challenging and somewhat daunting for new makers, there is a whole world of new applications opened up by getting comfortable with flexible filaments.
Try out a few fun test prints like bracelets, watches, or wallets to see if these materials are for you. As long as you are taking care of your printer, there is very little risk to trying out new print styles, and you might find a new favorite material to work with!