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SLA 3D Printing materials compared

Written by Maeli Latouche

SLA 3D Printing materials compared

Introduction

Stereolithography (SLA) can produce plastic parts with high resolution and accuracy, fine details, and a smooth surface finish. Thanks to the variety of resins available for SLA 3D printing, this process has found many applications in diverse industries:

In this article the most common SLA material options are presented. The key advantages of each SLA material are summarizes and actionable guidelines to help you choose the one that is most suitable for your application are presented.

An overview of the SLA materials

SLA uses a UV laser to cure liquid resin into hardened plastic in a process called photopolymerization. Different combinations of the monomers, oligomers, photoinitiators, and various other additives that comprise a resin result in different material properties.

SLA produces parts from thermoset polymers. Here are the main benefits and limitations that are common to all SLA materials:

Pros:

Smooth, injection mold-like, surface finish
Fine features & high detail
High stiffness

Cons:

Relatively brittle (low elongation at break)
Not suitable for outdoors use: the material properties may change over time, due overexposure to UV radiation (sunlight)
Susceptible to creep

In the following sections, we will go deeper into material properties that are specific to each SLA resin.

An extensive guide to the basic mechanics of the SLA 3D printing process can be found here. To learn more about designing parts for SLA, click here.

Curious about the cost and the available material options of SLA/DLP?

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Standard SLA resins

Standard resin

Standard resins produce high stiffness, high resolution prints with a smooth injection molding-like finish. Their low-cost makes them ideal for prototyping applications.

The color of the resin affects its properties. For example, grey resin is better suited for parts with fine details and white resin for parts that require a very smooth surface.

Pros:

Fine features & high detail
Smooth surface finish
Most economic SLA material

Cons:

Brittle (low elongation at break)
Low impact strength
Low heat deflection temperature

Ideal for: concept modeling, rapid prototyping, art models

Hearing aids 3D printed with SLA in Standard resin

Hearing aids 3D printed with SLA in Standard resin

Clear resin

Clear resin has similar mechanical properties to standard resin, but can be post-processed to near optical transparency.

More information on post-processing SLA parts can be found here.

Pros:

Fine features & high detail
Smooth surface finish
Transparent

Cons:

Brittle (low elongation at break)
Low impact strength
The optical clarity may change over time, as the part is exposed to UV radiation (sunlight)

Ideal for: showcasing internal features, LEDs housing, fluidic devices

An electronic enclosure 3D printed with SLA in Clear resin during different post-processing steps

An electronic enclosure 3D printed with SLA in Clear resin during different post-processing steps

Curious about the cost and the available material options of SLA/DLP?

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Engineering SLA resins

Engineering resins simulate a range of injection-molded plastics to provide engineers with a wide choice of material properties for prototyping, testing, and manufacturing.

All engineering resins require post-curing under UV light to reach their maximum mechanical properties

Tough resin (ABS-like)

Tough resin was developed for applications requiring materials that can withstand high stress and strain. Parts printed in tough resin have tensile strength (55.7 MPa) and modulus of elasticity (2.7 GPa) comparable to ABS.

This material will produce sturdy, shatter-resistant parts and functional prototypes, such as enclosure with snap-fit joints, or rugged prototypes.

Pros:

High stiffness
Excellent resistance to cyclic loads

Cons:

Not suitable for parts with thin walls (recommended minimum wall thickness of 1 mm)
Low heat deflection temperature
Relatively brittle (low elongation at break)

Ideal for: functional prototypes, mechanical assemblies

A quadcopter prototype 3D printed with SLA in Tough (ABS-like) resin

A quadcopter prototype 3D printed with SLA in Tough (ABS-like) resin. Image courtesy: Formlabs

Durable resin (PP-like)

Durable resin is a wear-resistant and flexible material with mechanical properties similar to Polypropylene (PP).

Durable resin can be used for parts that require high flexibility (high elongation at break), low friction and a smooth surface finish. Durable resin is particularly fitting for prototyping consumer products, snap fits, ball joints and low-friction moving parts.

Pros:

High wear resistance
Flexible (relatively high elongation at break)
High impact resistance (higher than Tough resin)

Cons:

Not suitable for parts with thin walls (recommended minimum wall thickness of 1 mm)
Low heat deflection temperature
Low tensile strength (lower than Tough resin)

Ideal for: functional prototypes, consumer products, low-friction and low-wear mechanical parts.

A toolcase with a hinge 3D printed with SLA in Durable (PP-like) resin

A toolcase with a hinge 3D printed with SLA in Durable (PP-like) resin. Image courtesy: Formlabs

Heat resistant resin

Heat resistant resin are ideal for applications that require high thermal stability and operate at high temperatures.

These resins have a heat deflection temperature between 200-300°C and are ideal for manufacturing heat resistant fixtures, mold prototypes, hot air and fluid flow equipment, and casting and thermoforming tooling.

To learn more about how 3D printing enables low-run injection molding, please refer to this article here.

Pros:

High heat deflection temperature
Smooth surface finish

Cons:

Brittle (low elongation at break)
Not suitable for parts with thin walls (recommended minimum wall thickness of 1 mm)

Ideal for: mold prototyping, casting and thermoforming tooling.

A mold 3D printed with SLA in Heat resistant resin

A low-run injection mold 3D printed with SLA in Heat resistant resin. Image courtesy: Formlabs

Rubber-like resin (Flexible)

Rubber-like resin allows engineers to simulate rubber parts that are soft to the touch. This material has a low tensile modulus and high elongation at break, and it is well-suited for objects that will be bent or compressed.

It can also be used to add ergonomic features to multi-material assemblies, like packagings, stamps, wearable prototyping, handles, overmolds and grips.

Pros:

High flexibility (high elongation at break)
Low hardness (simulates an 80A durometer rubber)
High impact resistance

Cons:

Lacks the properties of true rubber
Requires extensive support structures
The material properties degrade over time, as the part is exposed to UV radiation (sunlight)
Not suitable for parts with thin walls (recommended minimum wall thickness of 1 mm)

Ideal for: wearables prototyping, multi-material assemblies, handles, grips, overmolds

A model car tire 3D printed with SLA in Rubber-like (flexible) resin

A model car tire 3D printed with SLA in Rubber-like (flexible) resin. Image courtesy: Formlabs

Ceramic filled resin (Rigid)

Rigid resins are reinforced with glass or other ceramic particles and result in very stiff and rigid parts, with very smooth surface finish.

Rigid resins offer good thermal stability and heat resistance (Heat Deflection Temperature HDT @ 0.45MPa of 88°C). They have a high modulus of elasticity and lower creep (higher resistance to deformation over time) compared to other SLA resins, but are more brittle than the Tough and Durable resins.

Rigid resin is also suitable for parts with thin walls and small features (the recommended minimum wall thickness is 100 µm).

Pros:

High stiffness
Suitable for parts with fine features
Moderate heat resistance

Cons:

Brittle (low elongation at break)
Low impact strength

Ideal for: molds and tooling, jigs, manifolds, fixtures, housings for electrical and automotive applications

Thermal management components 3D printed with SLA in Ceramic filled (rigid) resin

Thermal management components 3D printed with SLA in Ceramic filled (rigid) resin. Image courtesy: Formlabs

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How to choose the right resin for your application

The table below summarizes the basic mechanical properties of the common SLA materials:

Standard & Clear Tough Durable Heat resistant Ceramic reinforced
IZOD impact strength (J/m) 25 38 109 14 N/A
Elongation at break (%) 6.2 24 49 2.0 5.6
Tensile strength (MPa) 65.0 55.7 31.8 51.1 75.2
Tensile Modulus (GPa) 2.80 2.80 1.26 3.60 4.10
Flexural Modulus (GPa) 2.2 1.6 0.82 3.3 3.7
HDT @ 0.45 MPa (oC) 73 48 43 289 88
Source: Formlabs

Standard resin has high tensile strength but is very brittle (very low elongation at break), so it is not suitable for functional parts. The ability to create fine features makes it ideal though for visual prototypes and art models.

Durable resin has the highest impact strength and elongation at break compared to the other SLA materials. It is best for prototyping parts with moving elements and snap-fits. It lacks though the strength thermoplastic 3D printing materials such, as SLA nylon.

Tough resin is a compromise between the material properties of durable and standard resin. It has tensile strength, so it is best suited for rigid parts that require high stiffness.

Heat resistant resin can withstand temperatures above 200oC, but has poor impact strength and is even more brittle than the standard resin.

Ceramic reinforce resin has the highest tensile strength and flexural modulus, but is brittle (poor elongation at break and impact strength). It should be prefered over other engineering resins for parts with fine features that require a high stiffness.

The following graphs representative mechanical properties of the most common SLA materials are visually compared:

Comparative chart for elongation at break and impact strength for common SLA engineering and standard materials
Comparative chart for elongation at break and impact strength for common SLA engineering and standard materials.

Image courtesy Formlabs

Stress-strain curves for common SLA engineering and standard materials
Stress-strain curves for common SLA engineering and standard materials.

Image courtesy Formlabs

Comparative chart of the material properties of the different engineering resins
Comparative chart of the material properties of the different engineering resins.

Image courtesy Formlabs

Dental & Medical SLA resins

Custom Medical Appliances Resin (Class I biocompatible)

Class I biocompatible resins can be used to make custom medical equipment, such as surgical guides. Parts printed in this resin can be steam sterilized using an autoclave, for a direct use in the operating room.

Pros:

High precision
Smooth finish
Class I biocompatible (short term use)

Cons:

Moderate wear and fracture resistance

Ideal for: surgical aids and appliances

Surgical dental guides printed with SLA in Custom Medical Appliances Resin

Surgical dental guides 3D printed with SLA in Custom Medical Appliances Resin. Image courtesy of Formlabs

Dental Long Term Biocompatible Resin (Class IIa biocompatible)

This resins are specially engineered for long term orthodontic appliances. Class IIa biocompatible resins can be in contact with the human body for up to a year.

Their high resistance to fracture and wear make it perfect to produce custom hard splints or retainers.

Pros:

High accuracy
High resistance to fracture and wear
Class II biocompatibility

Cons:

High cost

Ideal for: long term dental appliances, fracture and wear resistant medical parts, hard splints, retainers

Custom dental retainer 3D printed with SLA in Dental Long Term Biocompatible Resin

Custom dental retainer 3D printed with SLA in Dental Long Term Biocompatible Resin. Image courtesy of Formlabs

Class I vs Class IIa Biocompatibility

Class I biocompatibillity regulations refer to materials that are allowed to be used for:

Class IIa biocompatibility regulations refer to materials that are allowed to be used for:

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Castable SLA resins

Castable resin for jewellery making

This material enables printed parts with sharp details and a smooth finish, and will burn out cleanly without leaving ashes or residue.

Castable resin allows the production of parts directly from a digital design to investment casting through a single 3D printed part. They are suitable for jewellery and other small and intricate components.

Pros:

Low ash content after burnout (less than 0.02 %)
Fine features and high detail

Cons:

Low impact and wear resistance
Requires post-processing to ensure best results

Ideal for: investment casting, jewelry making

A ring master prototype before casting 3D printed with SLA in Castable resin

A ring master prototype before casting 3D printed with SLA in Castable resin

Rules of Thumb

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