Flexible filament

Flexible Filament: When to Use it and Which You Should Choose?

Flexible filament mimics the performance of various rubber types, letting you manufacture flexible and elastic components with a 3D printer.

3D printing’s unique ability to produce complex forms and geometries opens the door to countless possibilities with flexible materials, from soft contacts for machine tools to gaskets and inner grippers for robot arms.

This article explores flexible filament, including when to use it and the pros and cons.

Let’s jump in!

What is flexible filament?

Flexible filaments blend rigid plastic and rubber properties, creating a class of materials known as thermoplastic elastomers (TPEs).

Where things get confusing is TPE is also a material and a broader classification for soft materials. Simply put, it can be a filament or a classification.

TPU gasket
A TPU gasket printed with Ultimaker material

There are many physical and chemical property combinations for flexible materials. As a classification, TPEs cover various materials, including TPU (thermoplastic polyurethane) and TCP (thermoplastic co-polyester).

Some filaments are more elastic than others, and a material’s elasticity determines its stretchiness and elongation at break. Elasticity is significant because it determines how much a material can stretch before it deforms and breaks.

The most common flexible filament is TPU, or thermoplastic polyurethane, which has high elasticity ideal for industrial coatings and prototyping.

However, while some flexible filaments like TPU have rubber-like qualities, flexibility is also relative in the context of 3D printing. A tough semi-rigid material like polypropylene (PP) can bend and flex with impacts better than a hard material like ABS.

Flexible filaments pros and cons

The benefits of flexible filaments include the following:

  • High elasticity. Ideal for stretchy, bendable components.
  • High impact resistance. Ideal for casings, housings, and parts exposed to force.
  • Vibration and shock absorbance. Ideal for soft contacts and dampers.
  • Some flexible materials resist fatigue under cyclic loading, making them ideal for structural components.

However, there are a few drawbacks to flexible filaments:

  • Print imperfections. Flexible filaments are more prone to stringing, blobs, and failure on the print bed than rigid materials.
  • Low bridging performance, making overhangs and bridges tricky to print. This inevitably means the requirement for support material.
  • Limited post-processing capabilities – some flexible materials like TPU are unsuitable for polishing, although devices like the AMT PostPro SF50 can smooth TPU components with vapour.

When to use flexible filament?

Flexible filaments like TPU, TPE, and TPC are rubber and silicone substitutes for additive manufacturing, enabling the production of soft and elastic parts and tooling.

This makes flexible filament perfect for gaskets, O-rings, flexible caps, seals, bushings, soft contact points, grippers, and phone cases, although the elasticity and rigidity of the material determine its suitability for the application.

A shampoo bottle printed with Ultimaker PP

Another benefit is that even significant impacts do not usually deform products printed from flexible materials. For example, PP can substitute rigid thermoplastics in applications that demand impact resistance.

Flexible filament like TPU also absorbs shock with vibration-dampening qualities. It is also available in ESD-safe versions, making it suited to structural and electrical applications such as consumer electronics and robotics.

Choosing the best flexible filament

There are four main flexible filaments available:

Thermoplastic polyurethane (TPU)

TPU has high ductility and extreme abrasion resistance, making it perfect for functional, flexible parts and tooling. It exhibits high elongation at break with robust tensile strength, with greater hardness than TPE in most formulations.

Thermoplastic elastomer (TPE)

TPE can be softer, less rigid, and less dense than TPU, deforming more easily and closely mimicking the performance of soft silicone. It is the perfect material for lightweight, flexible seals and gaskets and products like phone cases.

Thermoplastic co-polyester (TPC)

TPC has lower elasticity and hardness than TPU but with greater density than TPE. It is suitable for parts requiring less elongation at break, making it ideal for flexible parts like protective covers, casings, and sleeves.

Polypropylene (PP)

PP is a semi-rigid plastic with excellent impact resistance and durability. It is tough, low-friction, and retains form after bending, making it perfect for semi-rigid applications such as packaging, bottles, and protective housings.

Find out more

For help choosing the flexible filament for 3D printing, please get in touch with the team at 01765 694 007 or email team@additive-x.com.

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Top image credit: Ultimaker.

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