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:

• Standard resins are used for general prototyping
• Engineering resins have specific mechanical & thermal properties
• Dental & medical resins have biocompatibility certifications
• Castable resins have zero ash-content after burnout

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:

Cons:

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.

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:

Cons:

Ideal for: concept modeling, rapid prototyping, art models

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:

Cons:

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

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:

Cons:

Ideal for: functional prototypes, mechanical assemblies

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:

Cons:

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

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:

Cons:

Ideal for: mold prototyping, casting and thermoforming tooling.

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:

Cons:

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

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:

Cons:

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

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 200^oC, 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:

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:

Cons:

Ideal for: surgical aids and appliances

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:

Cons:

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

Class I vs Class IIa Biocompatibility

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

• non-invasive devices that that come in contact with intact skin
• appliances for transient use or short-term use in the oral or ear canal or in nasal cavities
• reusable surgical instruments

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

• devices that come in contact with body fluids or open wounds
• devices used to administer or remove substances to and from the human body
• invasive short-term devices, such as invasive surgical elements
• long-term implantable devices placed in teeth

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:

Cons:

Ideal for: investment casting, jewelry making

Rules of Thumb

• Choose Standard resin for prototypes with a smooth injection molding-like surface finish.
• For functional prototypes, choose Tough resin if stiffness is your main design requirement, Durable resin for parts that need higher impact resistance or have moving parts, and Ceramic reinforced resin for parts with fine features.
• Rubber-like resin can produce parts with low hardness and high flexibility, but lack the performance of true rubber.
• Heat resistant resin can withstand temperatures above 200^oC, but are brittle.
• Class I biocompatible resins are suitable to come in external contact with the human body, while Class II biocompatible resins are suitable for short-term invasive devices.
• Castable resins have leave very little residues and ash content after burnout (less than 0.02%).