Can You 3D Print Rubber? Exploring Flexible and Elastic Materials for Additive Manufacturing

Rubber is an incredibly useful material that is elastic, flexible, impact resistant, and waterproof. These properties make rubber ideal for a huge range of applications from tires to gaskets to rubber bands. However, traditional rubber manufacturing relies on molding and curing techniques that are not compatible with 3D printing.

So can you actually 3D print using rubber materials? The short answer is yes, with some limitations. While pure rubber cannot be 3D printed, there are several alternative flexible and elastic materials that mimic properties of rubber. These materials allow designers to 3D print flexible objects with rubber-like qualities.

Challenges of 3D Printing Real Rubber

Natural rubber comes from latex harvested from rubber trees. It goes through a vulcanization process which transforms the raw latex into an elastic, moldable material. However, once rubber is vulcanized, it cannot be melted and reshaped like thermoplastics. This makes true rubber unsuitable for 3D printing processes like fused deposition modeling (FDM) which rely on heating and extruding materials.

Additionally, uncured liquid latex rubber has very low viscosity and would simply pour through the nozzle of a 3D printer before it could be layered and cured. So unfortunately, real rubber cannot be used directly in most desktop 3D printers today. The material properties that give rubber its strength and flexibility also prevent it from being compatible with additive manufacturing.

Flexible Thermoplastic Materials for 3D Printing

While pure rubber is off the table, there are several thermoplastic materials that can mimic properties of rubber for 3D printing flexible objects. Thermoplastic elastomers (TPE) and thermoplastic polyurethane (TPU) filaments are the most common options.

Thermoplastic Polyurethane (TPU)

TPU filament is one of the most popular materials for printing flexible objects on desktop FDM printers. TPU has elastic properties similar to rubber while still extruding and solidifying like a thermoplastic material.

TPU can stretch up to 5x its normal length. It is also highly impact resistant. These properties make it suitable for applications like shoe soles, phone cases, grips, gaskets, and flexible hinges. TPU has good abrasion resistance and layer adhesion.

The shore hardness of TPU filament ranges from 50A to 95A, with lower numbers being more rubber-like and flexible. 85A is a common hardness for general printing of flexible objects.

TPU does require higher temperatures of 220-250°C to print properly. A direct drive extruder is also recommended for flexible filaments. But overall, TPU is accessible for most hobbyist 3D printers.

Thermoplastic Elastomers (TPE)

Thermoplastic elastomers refer to a broad class of materials that exhibit both thermoplastic and elastomeric properties. This includes thermoplastic polyurethanes as well as other copolymers like TPEE (thermoplastic elastomer ester), TPES (thermoplastic elastomer styrene) and TPV (thermoplastic vulcanizate).

Like TPU, these elastomers can stretch and flex like rubber. They retain the thermoplastic ability to melt when heated and solidify when cooled. TPE filaments have lower melting points of 180-210°C, which makes them easier to print than TPU.

Flexible PLA Filaments

There are also modified PLA filaments blended with elastomers to increase flexibility while retaining the easy printability of PLA. These are marketed under names like “flexible PLA” or “PLA flex”. They are more rigid than TPU/TPE but provide some improved elasticity over pure PLA.

Other Flexible Materials

Some other notable thermoplastics with flexibility include:

• Ninjaflex – Very flexible TPE filament with 85A hardness. Requires direct drive extruder.
• Semiflex – TPVS material with 50A hardness. More flexible than TPU.
• Cheetah – TPE with 60A hardness. Flexible and fast printing.
• Filaflex – TPU material with 50A to 80A options.

Printers and Hardware Considerations

To 3D print using flexible filaments, there are some important considerations for your printer hardware:

• Direct drive extruder: Flexible filaments perform much better with a direct drive rather than a Bowden tube extruder. The direct drive provides better control and feed of the elastic filament.
• All-metal hot end: To print at the higher temperatures needed for TPU and other flexibles, an all-metal hot end is recommended. The Teflon tube in normal hot ends can deteriorate at temperatures above 240°C.
• Print surface: Flexible materials adhere less strongly to print beds. Using a PEI sheet or BuildTak surface will provide better adhesion. An enclosure can also help parts adhere during printing.
• Slower print speeds: Flexible materials need to be printed more slowly than rigid plastics, around 25-40mm/s for quality prints. This gives the material time to settle and bond between layers.
• Retraction settings: Retraction should be disabled completely when printing flexibles to avoid stripping the filament. Oozing can be minimized by reducing print temperature 5-10°C.

Applications for 3D Printed Flexible Materials

Here are some common uses cases and applications leveraging the elastic properties of TPU and other flexible filaments:

• Custom mechanical parts – Gears, cogs, pulleys that need torsional flexibility and impact resistance. The SainSmart TPU is well-suited for these dynamic mechanical applications.
• Prosthetic and orthotic devices – 3D printed prosthetic hands and custom orthotics are ideal applications for flexible and elastic materials to improve comfort and durability. The Formfutura TitanX TPU mimics the feel of human skin.
• Athletic shoe components – Midsoles, outsoles, and other shoe parts can be prototyped with flexible TPU materials like Fillamentum’s Edge TPU.
• Wearables – TPU and TPE materials are commonly used to make flexible brackets, watch bands, jewelry, and other wearable accessories.
• Phone cases – Flexible phone cases can easily be customized and printed as one piece with no assembly. TPU provides scratch resistance and shock absorption.
• Biomedical devices – Micron3DP’s Med 610 material has medical certifications for printing biocompatible, sterilizable parts like customized airway stents.
• Seals, gaskets, diaphragms – Replacement seals and gaskets for appliances can be quickly prototyped on any desktop 3D printer using a flexible material like NinjaFlex.
• Robotics parts – Flexible grippers and compliant actuators for robot hands have more dexterity when 3D printed with an elastic TPU material.

Limits of 3D Printed Flexibles

While TPU and TPE allow 3D printing many end-use flexible applications, there are some limitations to be aware of:

• Won’t match properties of real vulcanized rubber. 3D printed parts are more rigid.
• Low tear strength compared to molded rubber.
• Porous surface from layer lines. Needs smoothing for watertight applications.
• Limited chemical and environmental resistance.
• Can be difficult for complex geometries and thin walls.

If properties closer to real rubber are needed, companies like Chromatic 3D Materials and Wooto offer liquid silicone printing solutions. Photocentric also has a UV-curable liquid rubber resin. But these industrial systems are more expensive than desktop FDM printers.

The Future of Elastic 3D Printing Materials

Researchers are also exploring new methods and materials to improve 3D printing of stretchable objects. Here are two promising technologies on the horizon:

Liquid Crystalline Elastomers

Scientists at Georgia Tech have developed liquid crystal elastomers that can be 3D printed with over 700% elongation and full elastic recovery. The material aligns like a liquid crystal when heated during printing, then crosslinks into an elastic solid. This could enable 3D printing of complex and intricate rubber-like structures.

Vitrimer Elastomer Composites

Vitrimers are a class of plastics that can be repeatedly reshaped like thermosets while retaining mechanical strength like thermoplastics. Researchers at the University of Bristol combined vitrimers with an elastomer to create a composite that can be 3D printed into complex shapes. The material showed high flexibility and shape memory after being elongated over 150% of its initial length.

Conclusion

In summary, pure rubber remains out of reach for desktop FDM 3D printers today. But materials like TPU and other thermoplastic elastomers provide similar flexibility and elasticity for 3D printing applications that need rubber-like properties. As material science continues evolving, we may eventually see additive manufacturing of real vulcanized rubber. For now, the range of available flexible and elastic materials still open up enormous possibilities for 3D printing end-use flexible components.