EVERY RESIN WE RUN, WITH THE NUMBERS
Fourteen resins on a Formlabs Form 4, laid out the way an engineer picks a material: by the property that has to hold. Every figure below is Formlabs' published post-cured value for the formulation that actually runs on a Form 4 — which is not always the one in an older datasheet. If you just want a recommendation, the shorter chooser answers it in a line.
Build volume 200 × 125 × 210 mm · dimensional tolerance ±0.15% (min ±0.05 mm) up to 30 mm, widening on larger parts — see the SLA design guide.
WHAT EACH NUMBER ACTUALLY TELLS YOU
Material selection goes wrong when one number gets read in isolation. Strength without elongation picks a resin that shatters; stiffness without impact picks one that cracks at the first drop.
| PROPERTY | UNIT | WHAT IT MEANS | WHERE IT MISLEADS |
|---|---|---|---|
| Ultimate tensile strength | MPa | The stress the material takes before it breaks in tension. Higher = more load before failure, in a pure pull. | Says nothing about how it fails. Rigid 10K is the strongest resin here and also the one most likely to shatter. |
| Tensile / flexural modulus | MPa | Stiffness — how hard the material resists being stretched or bent. This is the number to read for 'must not flex'. | Stiffness and toughness pull in opposite directions. 9,900 MPa (Rigid 10K) feels ceramic; 660 MPa (Durable) feels like a milk bottle. |
| Elongation at break | % | How far it stretches before it snaps. The single best proxy for 'brittle or not'. | Under ~10% is brittle: it will chip at a support mark or crack when dropped. Over ~50% it bends and comes back. |
| Notched Izod impact | J/m | Energy absorbed by a notched bar when struck — resistance to cracking from an existing stress raiser. | Your part has notches whether you drew them or not: sharp internal corners, thread roots, support scars. Fillet them. |
| Heat deflection temp. (HDT) | °C | Temperature at which a loaded bar deflects by a set amount. Quoted at 0.45 MPa (light load) and 1.8 MPa (heavy load). | The 0.45 MPa figure is the headline; the 1.8 MPa figure is the one that matters if the part is carrying load while hot. High Temp is 238 °C at 0.45 MPa but 101 °C at 1.8 MPa. |
| Shore hardness | A / D | Surface hardness for elastomers. 40A is a soft silicone seal, 80A is a firm rubber bumper. | Hardness is not strength or tear resistance. A soft resin with poor tear strength rips at thin sections regardless of Shore number. |
- All figures are post-cured. A green part straight off the platform is far weaker. Cure state is part of the material spec, not an afterthought.
- These are test bars, not your part. Wall thickness, internal corners, support scars and orientation all reduce real-world strength. Use the numbers to rank materials, not to certify a design.
- Resins are thermosets and they age. Standard resins yellow and embrittle under UV, and every resin here creeps under sustained load. For outdoor or long-term structural parts, FDM in ASA or PC is usually the right answer.
START FROM THE CONSTRAINT
Write down the one thing the part must not do — flex, crack, melt, leak, spark — and the material list collapses to two or three options.
| THE PART… | RESIN | THE NUMBER THAT DECIDES IT |
|---|---|---|
| Must not flex under load | Rigid 4000, then Rigid 10K | Flexural modulus 3,400 → 9,900 MPa |
| Must survive being dropped or clamped | Tough 2000, or Tough 1500 for more give | Elongation 79% / 155%, notched Izod 25 / 42 J/m |
| Must hinge or snap repeatedly | Tough 1500, or Durable for low friction | Elongation 155% / 55% |
| Must hold shape near heat | High Temp, or Rigid 10K if it must also be stiff | HDT 238 °C @ 0.45 MPa (101 °C / 92 °C @ 1.8 MPa) |
| Must be transparent | Standard in Clear, polished or clear-coated | UTS 60 MPa, HDT 74 °C — the warmest of the standard colours |
| Must show the finest possible detail | Standard at 25 µm | 0.2 mm walls, 0.1 mm embossed features |
| Must be cheap and fast for a fit check | Fast Model at 200 µm | Roughly 2× the vertical speed of Standard |
| Must seal or damp like rubber | Flexible 80A firm · Flexible 50A soft · Silicone 40A softest | Shore 80A / 55A / 40A |
| Must be a real silicone (chemical + thermal) | Silicone 40A | 230% elongation, 500,000 Ross flex cycles |
| Must be static-safe | ESD | Dissipative surface, UTS 44.2 MPa |
| Must self-extinguish | Flame Retardant | UL 94 V-0 Blue Card, HDT 111 °C @ 0.45 MPa |
| Must burn out for investment casting | Castable Wax | 20% wax fill, clean burnout, printed at 25–50 µm |
RIGID RESINS, SIDE BY SIDE
Sorted the way you'd shortlist: general purpose first, then the ductile engineering resins, then the stiff and the specialist. HDT is quoted at 0.45 MPa.
| RESIN | ANALOGUE | UTS | MODULUS FLEX / TENSILE (MPa) | ELONG. | NOTCHED IZOD | HDT @0.45 | LAYERS | QUOTE |
|---|---|---|---|---|---|---|---|---|
| STANDARD TIER | ||||||||
| Standard | General-purpose acrylate | 60–62 MPa | 2,750 / 2,700 | 8–13% | 29–32 J/m | 62–74 °C | 25 / 50 / 100 µm | QUOTE › |
| Fast Model | Draft acrylate | 62 MPa | 2,740 / 2,670 | 11% | 37 J/m | 76 °C | 200 µm | QUOTE › |
| ENGINEERING TIER | ||||||||
| Tough 1500 | Polypropylene (PP) | 34 MPa | 1,370 / 1,460 | 155% | 42 J/m | 66 °C | 100 µm | QUOTE › |
| Tough 2000 | ABS | 40.4 MPa | 1,701 / 1,800 | 79% | 25 J/m | 70 °C | 50 or 100 µm | QUOTE › |
| Durable | Polyethylene (PE) | 28 MPa | 660 / 1,000 | 55% | 114 J/m | 41 °C | 50 or 100 µm | QUOTE › |
| Rigid 4000 | Glass-filled thermoplastic | 69 MPa | 3,400 / 4,100 | 5.3% | 23 J/m | 77 °C | 50 or 100 µm | QUOTE › |
| High Temp | High-HDT thermoset | 49 MPa | 2,800 / 2,800 | 2.3% | 17 J/m | 238 °C | 50 or 100 µm | QUOTE › |
| ESD | Static-dissipative acrylate | 44.2 MPa | 1,841 / 1,937 | 12% | 26 J/m | 62.2 °C | 50 or 100 µm | QUOTE › |
| SPECIALTY TIER | ||||||||
| Rigid 10K | Highly glass-filled thermoplastic | 88 MPa | 9,900 / 11,000 | 0.7% | 20 J/m | 238 °C | 50 or 100 µm | QUOTE › |
| Flame Retardant | UL 94 V-0 thermoset | 41 MPa | 2,700 / 3,100 | 7.1% | 22 J/m | 111 °C | 50 or 100 µm | QUOTE › |
| Castable Wax | 20% wax-filled pattern resin | 12 MPa | — / 220 | — | — | — | 25 or 50 µm | QUOTE › |
ELASTOMERS
Different properties matter here: hardness sets the feel, tear strength sets whether a thin section survives, and stress at 100% elongation tells you how hard it pushes back when stretched double.
| RESIN | SHORE | UTS | ELONG. | TEAR STRENGTH | STRESS @100% | LAYERS | QUOTE |
|---|---|---|---|---|---|---|---|
| Flexible 80A | 80 A | 10 MPa | 230% | — | — | 100 µm | QUOTE › |
| Flexible 50A | 55 A | 3.4 MPa | 160% | 12.3 kN/m | 1.7 MPa | 100 µm | QUOTE › |
| Silicone 40A | 40 A | 5.0 MPa | 230% | 12.0 kN/m | 1.0 MPa | 100 µm | QUOTE › |
Silicone 40A also survives 500,000 Ross flex cycles — the reason it gets used for seals that move, where an acrylate elastomer would fatigue.
ALL FOURTEEN, IN DETAIL
What each one is genuinely for, and the failure mode to design around. Standard resins are normally in stock; engineering and specialty resins are brought in per job, which carries a surcharge and a per-material minimum.
The detail resin. Crisp edges, smooth walls, the finish people picture when they picture resin printing. Clear polishes to near-optical transparency.
Visual prototypes, miniatures, display and concept models, light pipes and transparent parts, masters for moulding.
Brittle at 8–13% elongation — it chips at support marks and cracks if dropped. UV-sensitive: Clear yellows in sunlight, so it is an indoor material.
The same rigid-acrylate family as Standard, run at a coarse layer to get the part out of the machine fast — about 66 mm/hr of build height against Standard's 33 mm/hr.
Early iterations, form and fit checks, bulky models where surface finish is not the point.
We print it at 200 µm, so layer stepping is visible on shallow curves. Not a finish material and not a functional one.
The compliant engineering resin: stiff enough to hold a shape, ductile enough to bend a long way and spring back. 155% elongation is an order of magnitude past Standard.
Snap-fits, latches, flexures, clasps and buckles, self-tapping screw bosses, jigs that get handled.
Low heat tolerance (66 °C @ 0.45 MPa) and it creeps under sustained load — don't use it as a permanent structural bracket.
The strongest and stiffest of the Tough family — the closest SLA gets to a rugged ABS housing while still taking a knock.
Robust jigs and fixtures, protective shells, snap-fit enclosures, parts that need some creep resistance.
Still a thermoset: 70 °C @ 0.45 MPa. If the part lives in a car cabin or near a motor, look at FDM ASA or PC instead.
Pliable, lubricious and hard to crack — the lowest-friction resin in the range and the best notched impact figure of the rigid materials.
Living hinges, low-friction assemblies, gears and ball joints, squeezable prototypes, press-fit lids.
Softest of the rigid resins (660 MPa flex modulus) and only 41 °C HDT — it will sag in a hot car and deform under a sustained clamp.
Glass-filled, dimensionally stable and precise. Holds thin walls and fine geometry without bowing, and creeps far less than the standard resins.
Thin-walled housings, brackets, fixtures that must stay true, parts measured against a drawing.
5.3% elongation — it snaps rather than bends. Filled resins are also more abrasive on tanks, which is part of why it is special-order.
The heat resin: 238 °C heat deflection at 0.45 MPa, the highest in the range alongside Rigid 10K.
Moulds and tooling inserts, hot-air and hot-fluid channels, thermal testing, fixtures that sit near heat.
2.3% elongation and 17 J/m notched Izod — the most brittle material we print. It is a heat part, not a load part, and the 1.8 MPa HDT is 101 °C.
Bleeds static charge away instead of holding it, so it can be used around parts that a spark would kill.
Electronics assembly aids, component trays, board fixtures, tooling on an ESD-controlled bench.
If you are certifying to a standard, ask us for the datasheet's surface-resistance figures rather than assuming — the requirement is usually a band, not a threshold.
The stiffest material we print, by a distance: 9,900 MPa flexural modulus and 238 °C HDT. It feels like fired ceramic in the hand.
Short-run injection-mould inserts, wind-tunnel models, heat-and-load fixtures, parts that must not deflect at all.
0.7% elongation. It has essentially no give — design generous fillets, avoid press-fits, and expect it to shatter rather than bend if it is dropped.
Self-extinguishing and halogen-free, with a UL 94 Blue Card behind it — rare in a printable resin.
Electrical enclosures, interior rail and aerospace fixtures, anything near an ignition source or in a regulated cabinet.
7.1% elongation, so treat it as a rigid material. Certification applies to the material, not automatically to your part — tell us if you need the paperwork.
The firm elastomer — think a shoe sole or a bump stop. Resilient and tear-resistant rather than squashy.
Resilient bumpers, soft inserts and fixtures, shock-absorbing pads and grips, firm seals and gaskets.
Elastomers need thicker walls than you expect (1.5 mm+) and a longer cure; thin lips tear. The older V1 formulation quotes 8.9 MPa and 120% elongation — check which version a datasheet refers to.
Pliable and translucent, soft enough to squeeze between finger and thumb. Formerly sold as Elastic 50A.
Compliant features, compressible buttons, soft-touch grips, anatomy and medical-style models (non-clinical).
12.3 kN/m tear strength — thin membranes and sharp internal corners will rip. Supports leave marks that are hard to dress out of a soft surface.
A genuine 100% silicone — not an acrylate pretending. That brings silicone's chemical and thermal resistance and its fatigue life: 500,000 Ross flex cycles.
Seals and gaskets, grommets, soft wearables, overmould-style parts, anything that would normally be cast in silicone tooling.
The most demanding material in the range — dedicated tank, its own wash chemistry, 100 µm only, and a per-job minimum. Lead time is longer than everything else here.
A pattern material, not a part material: 20% wax fill that burns out cleanly with effectively zero ash for direct investment casting.
Jewellery patterns, fine filigree, small cast metal components, try-on models.
Soft and waxy by design (220 MPa tensile modulus) — patterns are fragile in transit. There is a per-part minimum on this resin because plate-time, not volume, sets the cost.
WHY EACH RESIN HAS ITS OWN LAYER OPTIONS
Layer height isn't a free quality dial. Each resin is only qualified at certain layer thicknesses, because cure depth, peel force and pigment loading all change with the formulation — which is why Silicone 40A is 100 µm only and Castable Wax runs fine at 25 µm.
Standard and Castable Wax only. Reserved for jewellery patterns, miniatures and anything where a curved surface has to look moulded. Roughly four times the layers of 100 µm, so expect the price to follow.
The default for most engineering resins when surface finish matters. A good compromise: stepping is barely visible on gentle curves.
What most resins quote at, and the only option for the elastomers and Tough 1500. Flat and vertical faces look identical to 50 µm; only shallow slopes show the difference.
Fast Model only. For fit checks where you care that the part exists more than how it looks.
Layer height only changes vertical resolution. Fine features in the XY plane — text, teeth, wall thickness — are set by the printer's optics and don't improve at a finer layer. Drop to 25 µm for the look of a curved surface, not to hold a tighter dimension.
THE REST OF THE FORMLABS CATALOGUE
Formlabs list around fifty resins. Most of the ones missing from this page are missing for a reason worth knowing before you spec one.
| MATERIAL | WHY NOT |
|---|---|
| Biocompatible: BioMed Amber / Black / Clear / White / Durable / Flex, Dental LT Clear & Comfort, Surgical Guide, Denture Base & Teeth, Premium Teeth, IBT & IBT Flex, Custom Tray, Soft Tissue, Permanent Crown, Temporary CB, BEGO VarseoSmile TriniQ | Biocompatible resins require a dedicated tank, build platform and finishing equipment kept isolated from every other material, plus the validated workflow and regulatory footing of a dental or medical manufacturer. We are a general engineering bureau and don't hold that setup — so we won't print them, including for 'non-clinical' use. |
| Ceramic: Alumina 4N | Printing is only the first half — the green part has to be debound and fired in a kiln on a controlled ramp, and it shrinks as it sinters. That's a separate ecosystem, not a resin swap. |
| Form 2 / Form 3-only resins: Grey Pro, Draft, Castable, Castable Wax 40, PU Rigid 650 & 1000, Ceramic, Model V2/V3 | These are formulated for older printers and older tanks. We run a Form 4 with Form 4 tanks — a Form 3-only resin has no Form 4 print profile and physically cannot be run here, however good the datasheet looks. |
| Clear Cast | It is an investment-casting pattern material whose name reads like 'the clear one'. It needs thick walls plus latticing and drain tooling we don't run, and we've had a customer order it wanting a transparent part. For anything transparent: Standard in Clear. |
| Colour Kit / Color Resin | Custom-pigmented resin means a bespoke cartridge per colour and a tank that can only ever run that colour. Coloured SLA parts are better served by printing in Standard and painting, dyeing or clear-coating afterwards. |
| Tough 1000 and True Cast | Both are current Form 4 materials we simply don't stock — Tough 1000 is the most ductile of the Tough family (180% elongation, HDPE-like), True Cast is a casting resin for heavier jewellery and components up to 5 mm thick. Ask if your job needs one; we can bring either in. |
WHAT HAPPENS AFTER THE PRINT
Parts come off the platform coated in uncured resin and go straight into isopropanol. Over-washing swells fine features and softens elastomers, so wash time is set per material, not per part.
Heat and UV together finish the polymerisation. Every number on this page is a post-cured number — an under-cured part can be less than half as strong. Elastomers and the engineering resins need longer and hotter cures than Standard.
SLA supports touch the part at small points and leave witness marks. We orient to keep them off critical faces, but on a cosmetic surface say so when you order and we'll plan the orientation around it.
Standard sands and primes well. Clear polishes or clear-coats to near-optical transparency. Filled resins (Rigid 4000, Rigid 10K) sand slowly and blunt abrasives; elastomers don't sand usefully at all.
FAQ
It depends what you mean by strong. Rigid 10K has the highest tensile strength (88 MPa) and by far the highest stiffness (9,900 MPa flexural modulus), but only 0.7% elongation, so it shatters rather than bends. If 'strong' means survives real-world handling, Tough 2000 (40.4 MPa, 79% elongation) or Tough 1500 (34 MPa, 155% elongation) will outlast it in almost every application.
High Temp Resin and Rigid 10K Resin both reach 238 °C heat deflection temperature at 0.45 MPa. Under real load the figures are much lower — 101 °C and 92 °C at 1.8 MPa — so tell us the load as well as the temperature. Standard resins soften from roughly 62–74 °C, and Durable from 41 °C.
No. Biocompatible materials need a dedicated resin tank, build platform and finishing equipment kept separate from everything else, and the validated workflow of a dental or medical manufacturer. We don't hold that setup, so we don't print BioMed, Dental LT, Surgical Guide, Denture, IBT, Premium Teeth or Custom Tray resins.
They're Formlabs' published values for post-cured test specimens, so treat them as a way to rank materials rather than as a guarantee for your geometry. Wall thickness, internal corners, support marks, orientation and how thoroughly a part is cured all move real-world strength — usually downwards.
Formlabs reformulates materials per printer generation, and the numbers move a long way. Tough 1500 V1 (Form 3) quotes 51% elongation; the V2 that runs on the Form 4 quotes 155%. Standard resins on the Form 4 are V5. If you're comparing against a datasheet, check it's the version your printer actually runs.
NOT SURE? SEND THE PART
Upload your model and tell us the constraint — the load, the temperature, the fit. We'll tell you which resin holds it, or say plainly if the part belongs on an FDM machine instead.