Flexible and elastic resins are soft photopolymers for SLA, DLP and masked-LCD (MSLA) printing. After post-cure they behave like rubber: they bend, stretch and return to shape. Grades are named by their Shore A hardness, typically from about 50A, comparable to a soft eraser, to about 80A, which feels like firm rubber. Softer grades, often called elastic, stretch further and spring back quickly; firmer grades, often called flexible, are stiffer and can recover more slowly.
Choose flexible resin when a soft part needs fine detail or a smooth surface that powder-bed and FDM elastomers cannot provide: soft-touch prototypes, small gaskets and seals, grips, buttons, masks and models that simulate overmolded rubber. Flexible resins are thermosets with lower tear strength and abrasion resistance than TPU or silicone; they stiffen in the cold and age under UV light. For durable rubber parts in production, molded silicone or TPU is the usual choice.
Mechanical and physical properties
| Property | Typical value | Notes |
|---|---|---|
| Hardness | ≈ Shore 50–80A | Grade-dependent; measured after full post-cure (ASTM D2240). |
| Tensile strength | ≈ 3–10 MPa | Softer grades at the lower end; molded TPU reaches ≈ 30–50 MPa. |
| Elongation at break | ≈ 100–300% | Lower than molded TPU or silicone; tears start at notches. |
| Tear strength | ≈ 10–25 kN/m | ASTM D624; well below molded TPU, so avoid sharp corners and thin lips. |
| Compression set | Low to moderate | Grade- and temperature-dependent; check the datasheet for sealing use. |
| Rebound and damping | Grade-dependent | Soft elastic grades spring back quickly; firmer grades often damp more. |
| Temperature sensitivity | High | Parts stiffen noticeably in the cold and soften when warm; check the service range. |
| Density | ≈ 1.0–1.2 g/cm³ | Cured resin. |
| UV and aging | Poor to moderate | Surfaces can yellow, harden or crack with sunlight and time. |
| Surface finish | Very good | Smooth and detailed; support marks are harder to remove cleanly than on rigid resin. |
Typical values for fully post-cured flexible and elastic grades, measured on printed specimens (ASTM D2240, D412 and D624). Values differ strongly between brands, hardness grades and post-cure conditions, and elastomer properties change with temperature and age. Use the datasheet of the grade named in your quote, and test seals and flexing parts under real conditions.
Printing flexible resins with SLA, DLP and MSLA
Soft resins are harder to print than rigid ones. Parts flex during printing and peeling, supports must hold a part that can sag, and washing has to stay short, because elastomeric resins absorb solvent and can swell or tear. After washing, parts are post-cured to reach their rated hardness and elongation. Design and ordering points:
- Wall thickness: plan about 1 mm as the minimum for firmer grades and more for the softest grades; thin soft walls sag during printing and tear during support removal.
- Corners and edges: tear strength is the main weakness, so round internal corners, avoid notches and give lips and flaps rounded edges.
- Orientation and supports: orient the part so supports land on non-critical faces. On soft parts, support marks are hard to sand away, so visible and sealing surfaces should stay support-free.
- Tall, slender features: soft parts sway as the platform moves; support or thicken these features, or split the part.
- Stiffness by design: hardness is fixed by the grade, but wall thickness, ribs, cutouts and lattices change how soft a part feels. DLP and SLA can print fine elastic lattices, provided uncured resin can drain.
- Hollows and lattices: closed cavities trap resin; leave drainage openings and avoid very fine closed cells.
- Combined parts: one print uses one resin, so rigid and soft assemblies are printed separately and bonded, or made by PolyJet, which jets several materials in one build.
Tolerances and surface
Without a tolerance on the drawing, Uretyco's default for SLA parts is ±0.2 mm or ±0.2%, whichever is greater. Flexible parts deform under the measuring force, so define how critical dimensions are measured, for example in a fixture or without load, and validate seals and fits on test parts. Surfaces are smooth and detailed; support marks and a slight surface tack on some soft grades are the main caveats.
Finishing options
The options are narrower than for rigid resin, because soft surfaces do not sand or polish well and coatings must stretch with the part.
| Finish | Effect | Notes |
|---|---|---|
| Supports removed | Lowest cost | Small marks remain; on soft grades, trimming works better than sanding. |
| Support marks trimmed and smoothed | Cleaner visible faces | Manual work; state which faces matter. |
| Flexible coating or paint | Color, less surface tack | Must be elastic; rigid paint cracks when the part flexes. |
| Bonding to rigid parts | Soft and rigid assemblies | Use adhesives suited to elastomers and test the joint. |
Flexible resin is a fast way to check the feel, fit and sealing of a soft part before tooling. For production quantities, the same geometry can be molded in silicone or TPU, which gives far higher tear strength and a longer service life.
Cost and lead-time drivers
Flexible resins cost more per liter than standard resin, and soft parts print more slowly and need more careful handling. The main drivers:
- Resin volume and height: solid soft parts use more resin, and build height drives print time.
- Print speed: many flexible grades need slower settings so soft layers do not tear or deform.
- Support removal and cleanup: soft parts are trimmed by hand, which adds labor on complex shapes.
- Robust geometry: thin, soft features fail more often during printing and support removal; robust geometry keeps cost and lead time predictable.
- Batching: small parts such as seals and buttons can be nested in one build, especially on DLP and MSLA.
Flexible resin vs. other options
| Material and process | Hardness range | Tear and abrasion | Detail and surface | Best for |
|---|---|---|---|---|
| Flexible resin (SLA, DLP, MSLA) | ≈ Shore 50–80A | Moderate tear strength, low abrasion resistance | Excellent; fine detail | Soft prototypes, small seals, fine elastic details |
| TPU 95A (MJF, FDM) | Shore 95A; softer FDM grades exist | Excellent | Grainy (MJF) or layer lines (FDM) | Durable, functional flexible parts |
| TPE (FDM) | ≈ Shore 60–90A | Lower than TPU 95A | Visible layer lines | Soft grips, feet and dampers |
| PolyJet rubber-like (such as Agilus) | ≈ Shore 30–95A | Low | Excellent; combines with rigid material | Overmold look-alikes, multi-material prototypes |
| Silicone (LSR or cast) | ≈ Shore 10–80A | Good tear strength in high-tear grades; moderate abrasion resistance | Defined by the mold | Production seals, heat and long-term compression |
Choose flexible resin for small, detailed soft parts and quick feel tests. TPU suits flexible parts that must withstand abrasion and repeated use, PolyJet rubber-like materials suit prototypes that combine rigid and soft regions in one part, and for production seals and grips, molded silicone or injection-molded TPU is the usual route.
When not to choose flexible resin
Parts exposed to abrasion, sliding or repeated stretching over long periods: use TPU or a molded rubber. Long-term static seals, especially when warm: use silicone or a molded elastomer. Cold or heat outside the rated range of the grade. Outdoor use: UV exposure hardens and cracks the surface. Skin-contact, wearable or medical use: only grades certified for that purpose and processed exactly as specified are suitable. Large, bulky soft parts, which are slow and costly to print and hard to support.
Typical applications
- Soft-touch prototypes, grips and handles.
- Prototype gaskets and seals for fit and sealing tests.
- Buttons, keypads and membranes with fine detail.
- Prototypes that simulate overmolded rubber on rigid parts.
- Cushioning lattices and damping elements printed by DLP or SLA.
- Anatomical and training models with a soft-tissue feel.
Specifying flexible resin on Uretyco
- 1Upload STL or 3MF
Use a fine mesh and check units; add a drawing if sealing dimensions or fits are critical.
- 2State the hardness
Give the target Shore A value, for example 50A or 80A, or describe the feel you need; the quote proposes a matching grade.
- 3Describe the use
Note sealing, stretching, repeated flexing, temperature and any skin contact so the assistant can flag a mismatch with resin.
- 4Mark critical faces
Mark sealing lips and visible faces that must stay free of support marks, and state how critical dimensions should be measured.
- 5Review the quote
Check the confirmed grade, technology and lead time; specialized grades are confirmed during quote and order review.
FAQ
Which Shore hardness should be chosen?
About 50A for soft, compliant parts such as cushions, soft seals and skin-like surfaces; about 70–80A for firmer gaskets, grips and buttons that must hold their shape. Geometry changes the feel as well: thin walls and cutouts make any grade feel softer.
Can flexible resin be used for seals and gaskets?
For prototypes and for low-pressure seals at room temperature, yes. Sealing faces should be support-free, and the design should be tested for leak-tightness. For long-term static seals, or seals exposed to heat, oil or weather, molded silicone or another molded rubber is more durable.
Flexible resin or TPU?
Flexible resin offers finer detail, softer grades and a smoother surface. TPU printed by MJF or FDM is much tougher, with far higher tear and abrasion resistance, so it suits functional parts that are handled and flexed often. When a part is feasible in both, the quote can compare them.
How long do flexible resin parts last?
Not as long as molded rubber. Flexible photopolymers slowly harden and can crack under UV light, heat and repeated flexing, and tears grow from small notches. Treat them as prototypes or short-life parts unless the datasheet of the grade and your own tests support longer use.
Related resources
- TPU 95ATough flexible parts by MJF, FDM or molding.
- TPESoft FDM filament for grips, feet and dampers.
- PolyJet Rubber-likeSoft and rigid regions in one printed part.
- Liquid Silicone Rubber (LSR)Production seals for heat and compression.
- Silicone MoldingSoft tooling and silicone production routes.
- 3D PrintingTechnologies, tolerances and cost drivers.
Related materials
Plastics
Standard SLA
General-purpose photopolymer for SLA and DLP printing: the smoothest surfaces and finest detail of any common 3D printing process, but brittle and heat-sensitive. The default for cosmetic prototypes, detailed models and casting masters.
Plastics
Clear Resin
Unpigmented photopolymer for SLA, DLP and MSLA that prints translucent and becomes close to transparent after sanding and polishing or a clear coat. For see-through prototypes, fluidic models and light covers; brittle and prone to yellowing.
Plastics
Dental Resin
Photopolymers for dentistry: accurate model resins and biocompatible grades for guides, splints and temporary crowns. Use in the mouth depends on the certified resin, a validated printer and post-processing workflow, and the device maker's regulatory duties.
Plastics
High-Temp Resin
Heat-resistant photopolymer for SLA and DLP printing, reaching an HDT of roughly 100–250 °C or more after thermal post-cure. Used for low-volume mold inserts, heat-exposed fixtures and hot air or fluid flow tests; stiff but brittle.
Plastics
Tough Resin
Engineering photopolymers formulated to behave like ABS or polypropylene: far more impact- and fatigue-tolerant than standard resin, with the same smooth surface and fine detail. For snap-fits, enclosures, jigs and functional prototypes at room temperature.
Elastomers
TPU 95A
Tough, abrasion-resistant thermoplastic elastomer with a firm, rubber-like Shore 95A hardness. Printed by MJF or FDM, or injection-molded, for grips, bumpers, covers, light-duty seals and cushioning.
Can't find what you need? Contact our team for expert assistance with your manufacturing project.