SLA – Flexible 50A Resin
Flexible 50A is a soft, 50 Shore A resin for SLA 3D printing, made for prototyping parts that would normally be molded in silicone. It is one of the softest SLA materials available. Formlabs previously sold it as Elastic 50A. Parts can bend, stretch, and compress through repeated cycles and return to their original shape without tearing, with a smooth, translucent finish.
What Flexible 50A Is Best For
- Prototypes of soft silicone and rubber parts
- Compliant features for robotics and grippers
- Seals for vacuum and pressure test tooling
- Wearables and consumer product prototypes
- Compressible buttons
- Medical models and devices
- Special effects props and models
- Low-quantity production of small soft parts
When another material is a better fit
- Need true silicone: Silicone 40A
- Need a firmer rubber-like part: Flexible 80A
- Need a tougher, more durable rubber-like part, or a part that will live outdoors: MJF TPU
Key Material Facts
- Shore hardness: 50A nominal (55A measured), one of the softest SLA materials
- Elongation at break: 160%
- Tear strength: 12.3 kN/m
- Low compression set: 2.1% at 23°C and 3.1% at 70°C (22 hours)
- Holds up to repeated bending, stretching, and compressing
- Smooth, translucent surface
- Resists water, salt water, bleach, mild acids and bases, and mineral oil; swells significantly in fuels, alcohols, and most solvents (see the solvent table below)
- Fine for indoor use; long-term outdoor exposure breaks it down (see our weather test below)
SLA Flexible 50A Material Properties
Version note: we currently print with the latest formulation of this resin, which Formlabs previously sold as Elastic 50A V2 and now sells as Flexible 50A.
Mechanical properties (post-cured, from Formlabs’ published Flexible 50A data sheet)
| Property | Metric | English | Method |
|---|---|---|---|
| Ultimate tensile strength | 3.4 MPa | 487 psi | ASTM D412-06 (A) |
| Stress at 50% elongation | 0.9 MPa | 134 psi | ASTM D412-06 (A) |
| Stress at 100% elongation | 1.7 MPa | 246 psi | ASTM D412-06 (A) |
| Elongation at break | 160% | 160% | ASTM D412-06 (A) |
| Tear strength | 12.3 kN/m | 70.2 lbf/in | ASTM D624-00 |
| Shore hardness | 55A | 55A | ASTM 2240 |
| Compression set (23°C for 22 hours) | 2.1% | 2.1% | ASTM D395-03 (B) |
| Compression set (70°C for 22 hours) | 3.1% | 3.1% | |
| Bayshore resilience | 18% | 18% | ASTM D2632 |
Solvent compatibility: percent weight gain over 24 hours for a printed and post-cured 1 × 1 × 1 cm cube immersed in each solvent.
| Solvent | 24 hr weight gain, % |
|---|---|
| Acetic acid 5% | 1.5 |
| Acetone | 43.4 |
| Bleach ~5% NaOCl | 0.6 |
| Butyl acetate | 133.1 |
| Diesel fuel | 7.9 |
| Diethyl glycol monomethyl ether | 31.4 |
| Hydraulic oil | 3.9 |
| Hydrogen peroxide (3%) | 0.9 |
| Isooctane (gasoline) | 15.6 |
| Isopropyl alcohol | 39.2 |
| Mineral oil (light) | 0.7 |
| Mineral oil (heavy) | 0.4 |
| Salt water (3.5% NaCl) | 0.6 |
| Skydrol 5 | 41.2 |
| Sodium hydroxide solution (0.025%, pH 10) | 0.7 |
| Strong acid (HCl, concentrated) | 45.6 |
| Tripropylene glycol monomethyl ether (TPM) | 43.6 |
| Water | 0.7 |
| Xylene | 163.9 |
More information is available from Formlabs, the material manufacturer.
Outdoor UV and Weather Testing
We left parts printed in the original Elastic 50A (V1) resin outside from July 2023 to February 2024 to see how the material holds up to long-term UV exposure and weather, including rain and snow.
Fresh parts, July 2023:
Outdoor-aged parts, February 2024 (7 months):
After 7 months outdoors, the parts held up reasonably well, but with rough handling they started to tear and break down.
Indoor-aged parts, February 2024 (7 months): we kept another set inside our building, next to a window but out of direct sunlight. These parts yellowed less, stayed stronger, and could be handled roughly without tearing.
Finish and Color Options
Flexible 50A parts ship translucent, with supports removed and the parts cleaned and post-cured. No additional finishes are offered for this material. See all of our finishing and post-processing options.
Flexible 50A Part Gallery
Related Resources
- SLA 3D printing overview
- SLA part design guide
- 3D printed vacuum blocks
- Accuracy of 3D printed parts
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