Formlabs Silicone 40A Resin: What Makes It Different from Flexible Resins?

When you need to 3D print a soft, flexible part, there are many materials to choose from. Flexible and elastic resins can produce parts that bend, stretch, and compress, but not all flexible materials are silicone.

That distinction is important when a finished part needs the characteristic properties of silicone, such as flexibility, durability, chemical resistance, and thermal stability.

Formlabs Silicone 40A Resin takes a different approach. Rather than producing a silicone-like material, it is a 100% silicone 3D printing material designed for the Formlabs SLA ecosystem.

So, what makes Silicone 40A different from conventional flexible resins, and when should you consider using it?

What Is Formlabs Silicone 40A Resin?

Formlabs Silicone 40A Resin is a specialty material developed using Formlabs' Pure Silicone Technology™.

According to Formlabs, it is a pure silicone material without added monomers or acrylates. This allows users to produce silicone parts directly through 3D printing rather than first creating a mold and casting the silicone.

The material has a 40A Shore hardness, making it soft and pliable while still providing durability for repeated flexing, stretching, and compression.

Its published properties include:

• 40A Shore hardness

• 230% elongation at break

• 12 kN/m tear strength

• 5 MPa ultimate tensile strength

• More than 500,000 Ross flexing fatigue cycles

• -25°C to 125°C thermal stability

• Features as small as 0.3 mm can be produced under Formlabs' stated conditions.

These characteristics make it suitable for functional silicone parts rather than simply flexible-looking prototypes.

Silicone vs Flexible Resin: What's the Difference?

The most important difference is what the material actually is.

A flexible resin can be formulated to behave like rubber or elastomeric material after printing. For example, Formlabs' Elastic 50A Resin is an acrylic-based elastomeric material.

Silicone 40A, on the other hand, is pure silicone.

Formlabs specifically describes Elastic 50A as an acrylic-based elastomer, while Silicone 40A is its pure silicone material.

That difference affects how you should think about the two materials.

The comparison isn't simply about which material is "more flexible." The better choice depends on the properties required by the finished part.

Why Does 100% Silicone Matter?

Silicone has properties that make it useful in applications where ordinary flexible polymers may not be the best fit.

Silicone is widely used for components that need to repeatedly flex, compress, stretch, or maintain performance under demanding environmental conditions.

With Silicone 40A Resin, Formlabs combines those characteristics with the design freedom of SLA 3D printing.

This opens up possibilities for producing customized silicone components without traditional tooling.

1. No Traditional Mold Required

One of the biggest advantages of Silicone 40A is the ability to produce silicone parts directly from a digital design.

Traditional silicone manufacturing often involves creating tooling or molds before casting the material.

With 3D printed Silicone 40A, you can go from CAD design to a printed silicone component without first creating a dedicated mold. Formlabs positions this as a way to eliminate tooling and labor-intensive casting processes for custom and low-volume production.

This can be especially useful when:

• Only a small number of parts are needed

• The design changes frequently

• The geometry is difficult to mold

• Customized parts are required

• You need to prototype quickly

2. Designed for Repeated Flexing

Flexible materials are often selected because a component needs to bend or deform without immediately failing.

Silicone 40A is specifically designed for repeated stretching, flexing, and compression.

Formlabs reports more than 500,000 Ross flexing fatigue cycles under its specified test conditions.

This makes the material interesting for components that experience repeated movement rather than being flexed only occasionally.

Potential applications include:

• Gaskets

• Seals

• Dampeners

• Grippers

• Wearables

• Flexible connectors

• Soft fixtures

3. 40A Shore Hardness

The "40A" in Silicone 40A refers to its Shore A hardness.

Shore A is commonly used to describe the hardness of softer elastomeric materials.

A 40A material is relatively soft and pliable, allowing printed parts to deform under pressure.

This makes Silicone 40A appropriate for applications where you need a component that can:

• Compress

• Bend

• Stretch

• Conform to another surface

• Return toward its original shape

The exact behavior of a finished part will also depend on its geometry, wall thickness, infill or internal structure where applicable, and print orientation.

4. High Elongation and Tear Strength

Two important properties for flexible components are elongation and tear strength.

Silicone 40A has a reported 230% elongation at break, meaning the material can undergo substantial stretching before breaking under the specified test conditions.

It also has a reported 12 kN/m tear strength.

Together, these properties help make Silicone 40A suitable for parts that need to deform repeatedly without being excessively fragile.

5. Chemical and Thermal Resistance

Another important distinction is environmental performance.

Formlabs specifies Silicone 40A Resin as having excellent chemical resistance and thermal stability from -25°C to 125°C.

That can make it useful for applications where a soft component may encounter:

• Temperature changes

• Oils or chemicals

• Repeated mechanical movement

• General industrial environments

As always, compatibility should be evaluated for the specific chemical, temperature, exposure time, and application rather than assuming universal resistance.

What Can You Make with Silicone 40A?

The combination of flexibility, durability, and silicone material properties makes the resin useful across several industries.

Seals and Gaskets

Custom seals and gaskets are natural applications for a soft elastomer.

The ability to create customized geometries without conventional tooling can be particularly useful for prototypes, replacement designs, and low-volume parts.

Robotics

Robotic systems can use soft components such as grippers, dampeners, and flexible connectors.

Silicone 40A can help designers create customized components around specific robotic mechanisms.

Wearables

Soft, flexible components can be useful for wearable products where the material needs to conform to surfaces or withstand repeated movement.

Manufacturing Aids

Formlabs lists flexible fixtures, masking tools, and soft molds among applications for Silicone 40A.

Medical and Healthcare Applications

Formlabs also identifies applications including customized prosthetics, orthotics, audiology models, and medical devices.

Specific medical applications should always be evaluated against the relevant regulatory and biocompatibility requirements.

Silicone 40A vs Elastic 50A

If you're deciding between two Formlabs elastomeric materials, it helps to understand the fundamental difference.

Silicone 40A is a pure silicone material with a 40A Shore hardness. It is designed for functional silicone parts, including applications that benefit from durability, chemical resistance, and thermal stability.

Elastic 50A, by comparison, is an acrylic-based elastomeric material with a 50A Shore hardness. Formlabs positions it toward rapid prototyping and applications where a soft, elastic material is needed.

In simple terms:

Choose Silicone 40A when the properties of actual silicone are important.

Choose an elastic/flexible resin when you primarily need a flexible prototype and don't specifically require silicone.

Why 3D Print Silicone Instead of Casting It?

Traditional silicone casting remains useful for many applications, especially when producing large quantities.

But direct 3D printing can offer advantages during development and low-volume production.

Traditional Casting

Typically involves:

1. Designing a mold

2. Manufacturing the mold

3. Preparing silicone

4. Casting the material

5. Removing and finishing the part

3D Printing with Silicone 40A

The workflow can instead begin with:

1. Create or modify the CAD model

2. Prepare the file for printing

3. 3D print the silicone part

4. Wash and post-cure the part

5. Finish and inspect the component

The result is greater freedom to produce customized and complex geometries without committing to dedicated tooling. Formlabs specifically highlights complex geometries and custom or low-volume manufacturing as key applications for Silicone 40A.

Is Silicone 40A Right for Your Project?

Silicone 40A is worth considering when you need actual silicone properties, not simply a flexible 3D-printed material.

It can be a good fit for projects involving:

• Soft functional components

• Custom seals and gaskets

• Flexible connectors

• Grippers

• Dampeners

• Wearables

• Soft molds

• Flexible fixtures

• Low-volume silicone parts

• Complex silicone geometries

On the other hand, if you're primarily looking for a flexible prototype, an acrylic-based flexible or elastic resin may be sufficient.

Formlabs Silicone 40A Resin for Form 4

DigitMakers carries Formlabs Silicone 40A Resin (Form 4) 1 L, with compatibility listed for Form 4 and Form 4B as well as certain Form 3 platforms. The product page lists the Form 4 Resin Tank and Form 3 Resin Tank V2.1 as compatible tanks.

You can find the product here:

Formlabs Silicone 40A Resin (Form 4) 1 L 

Final Thoughts

The biggest difference between Formlabs Silicone 40A Resin and conventional flexible resins comes down to the material itself.

Flexible resin can give you a soft, rubber-like part. Silicone 40A gives you a 100% silicone part.

With its 40A Shore hardness, 230% elongation at break, 12 kN/m tear strength, and thermal stability from -25°C to 125°C, Silicone 40A is designed for applications where flexibility needs to be combined with the functional properties of silicone.

For designers and engineers working on custom silicone components, prototypes, manufacturing aids, or low-volume production, direct silicone 3D printing can eliminate some of the tooling and casting steps traditionally associated with silicone parts.

If your project needs the properties of real silicone and the design freedom of 3D printing, Formlabs Silicone 40A is a material worth exploring.