Flexible 3D Printing Guide: Compare Processes, Materials, and Applications

FDM 3D printing, where a nozzle melts a spool of hard plastic filament and extrudes it through a nozzle to build the shape layer by layer, is perhaps the most well-known type of 3D printing due to its low entry-level price point and easy-to-grasp technology. There are many different types of FDM materials available, including several flexible filaments.

The benefits of FDM 3D printing with flexible filament are that you can easily and inexpensively produce simple flexible parts or prototypes. Flexible FDM 3D printed parts have good elasticity, impact resistance, vibration or shock absorption, and elongation. These qualities make FDM 3D printing flexible filaments ideal for early-stage prototypes of dampeners, actuators or end-of-arm tooling, soft casings, and stretchable enclosures.

However, because the flexible filament retains some of these stretchy properties even in its melted state during extrusion, there are often print quality issues when FDM 3D printing flexible materials. Design features such as overhangs and bridges often lead to issues like stringing, uneven surface finish, clogged extruders, and poor mechanical performance. Because FDM 3D printed parts are not chemically isotropic in the Z-axis direction, layers can separate during elongation. If the part’s purpose is to stretch and bounce back, that separation will often result in part failure. 

Additionally, any jerkiness or accidental deviation from the programmed path of the extruder can negatively impact the way the flexible filament sets — these flexible filaments are more prone to poor adhesion than rigid filaments, so users should be aware that the printer has to to remain perfectly steady and the nozzle and extruder should move very slowly to give the flexible filament adequate time to extrude and set.

Most FDM 3D printers are compatible with some type of flexible filament. A good practice to narrow the search for an FDM printer that is more suited to flexible materials is to look for one that is capable of heating the extruder up to around 220 °C and has a heated bed, a direct drive extruder (to minimize stringing), controllable feed rates (to modify the speed at which the flexible filament is extruded), and a cooling fan.

Flexible 3D printing filaments can all be classified as thermoplastic elastomers (TPE) because they are altered by heat and display elastomeric properties, though TPE can also refer to a specific type of filament. The five most common flexible 3D printing filaments are: 

TPU (thermoplastic polyurethane): TPU is one of the most common types of flexible filament. It is strong, can handle shocks and general wear and tear from use, and can come in various colors. Many products that may seem to be rubber are actually made from TPU. TPU is slightly more rigid than other thermoplastic elastomers, and is, therefore, the easiest flexible 3D printing filament to print with, as there is less chance of it stringing or oozing. FDM 3D printing with a flexible TPU filament is helpful in early-stage prototyping, but for functional prototypes and end-use parts, its anisotropic qualities can lead to inferior performance. 

TPC (thermoplastic co-polyester): TPC is a polyester-based flexible 3D printing filament with good thermal stability and chemical resistance, but is less flexible than other TPEs. Some common examples of TPC parts are bumpers, flexible air-ducting, and softer casings, covers, and enclosures made to protect from compression or shock. When printing with TPC, it’s important to bring the material to an ambient temperature before loading the printer, use a direct-drive extruder, and make sure to have an extruder temperature capability of at least 230 °C. 

TPA (thermoplastic polyamide): TPA is a chemical co-polymer of TPE and flexible nylon that is smooth and highly flexible. This combination of two commonly known flexible 3D printing materials leads to a filament that is smooth, soft, and flexible. TPA can withstand repeated shock or pressure, and is very durable. Parts that need to be repeatedly twisted, bent, or stretched can be printed in TPA — these properties make TPA ideal for functional prototypes, wearables, and engineering components. Most TPA filaments have a shore hardness of around 80A, which is similar to what you might often think of as rubber. 

TPE (thermoplastic elastomer): As mentioned above, TPE can refer to the entire group of elastomeric thermoplastics, or a specific material. TPE filament is very elastic and soft, and is harder to print with than its more rigid counterpart, TPU. The TPE flexible filament is prone to oozing, or becoming overheated and unable to hold the nozzle shape, and should therefore be printed very slowly with a 3D printer that can easily and precisely control extruder temperature. TPE flexible filament is a good material choice for 3D printing wearables like wristbands or consumer goods like phone cases that can be stretched around the device. 

Soft PLA: Soft PLA is a flexible filament made from organic fibers treated with chemicals. It can hold a rigid shape easily, but will return to its original shape after experiencing pressure. For this rigidity, it’s commonly used for items like tire prototypes or tough rubbery parts that need to maintain their shape and format the majority of the time. While soft PLA is one of the easiest flexible filaments to print with, it's more prone to jamming the extruder, and printing speed should be reduced. 

Resin 3D printers, such as stereolithography (SLA) 3D printers, use a laser or other light source to cure a liquid vat of plastic one layer at a time, and offer many options for flexible 3D printing materials. 

Resin 3D printer manufacturers mostly manufacture their own materials — so they aren’t as easy to identify and group as FDM 3D printing flexible filaments. However, they all share similar characteristics and printing considerations, and can be used for a wide range of applications in many industries. 

Selective laser sintering (SLS) refers to the powder bed fusion 3D printing process where a laser fuses powder particles layer by layer. The unused material supports the parts during printing so you can create complex, interconnecting designs with no need for support structures. Much like with FDM 3D printing, SLS 3D printing manufacturers offer powders that are familiar and well-understood in the engineering world, such as nylon and TPU.

One of the advantages to additive manufacturing is the ability to choose a material for your specific application — there are so many different filaments, resins, and powders available. For flexible 3D printed parts that behave like traditionally fabricated rubbers, silicones, or thermoplastic elastomers, there are multiple technologies, manufacturers, and materials to choose from. 

The Formlabs SLA ecosystem makes flexible resin 3D printing easy and intuitive through the combination of reliable hardware and specialized, advanced materials developed for targeted applications and industries. There are a wide range of flexible materials available for the Form 3/B/+ and Form 3L/3BL ecosystems — including biocompatible materials that enable new applications in healthcare and medical device manufacturing. The post-processing steps are also handled cleanly and simply by automated post-processing solutions, making flexible resin 3D printing easy and clean.