Flexible / elastomeric resins (405 nm LCD/DLP)

Published · Researched 2026-09-20

Overview — what it is, best uses, key context

Flexible resins are photopolymers that cure into rubber-like parts: gaskets, seals, vibration dampers, grips, wearable prototypes, and soft robotics components. They span hard-flexible (Shore 65D, bendable but firm — Siraya Tenacious) down to true elastomers (Shore 70A and softer — Tenacious Flex Black, Formlabs Flexible 50A) that stretch and rebound. Best uses: parts that must bend 180°, compress repeatedly, or absorb impact without shattering — the resin counterpart to TPU filament. Two usage modes exist: print straight (softest results) or blend 10–30% into rigid resins (the famous Tenacious trick: a splash of Tenacious in standard resin dramatically improves impact resistance while keeping detail).

Current 2026 products and brands

• Siraya Tech Tenacious 65D (flex-tough hybrid): from $44.85 sale / $65.00 list — siraya.tech sales page (fresh), obs. 2026-09-20. A second category crawl showed from $25.19 / $35.99 — variant/size ambiguity between the two pages (flagged; likely different bottle sizes). Thin parts "can bend 180° without shattering" (manufacturer/reseller copy); printable at ≥25 °C ambient (Siraya guidance).
• Siraya Tech Tenacious Flex Black 70A (soft elastomer): from $32.49 sale / $49.99 list — siraya.tech; 1 kg $69.99 at WoodArtSupply (fresh); old Amazon crawl $46.54/$69.99 (278 days prior — stale).
• Formlabs Flexible 50A (true elastomer, translucent): $219.00 / 1 kg (Form 3) — dynamism.com (crawled 1 day prior), obs. 2026-09-20; v2 cartridge 5 L (Form 3/4, contact pricing, 15 L minimum order). "Bend, stretch, compress, hold up to repeated cycles without tearing, spring back quickly" (Dynamism/Formlabs copy). Form 3/4-only.
• Formlabs Flexible 80A (firmer flex): £170 ex VAT — 2022 UK pricelist (1451 days old — stale; current price UNVERIFIED).
• Formlabs BioMed Flex 50A (biocompatible flex): $389.00 / 1 L — dynamism.com (crawled 1 day prior) — covered in depth in dental-resins.md.

Key specs (documented)

What's needed (hardware)

• 405 nm MSLA printer (Tenacious/Flex Black work on any; Formlabs resins are Form 3/4-locked).
• Warm room (≥25 °C) — cold flexible resin prints fail (Siraya guidance). A printer enclosure or heated space matters more here than for rigid resins.
• Standard resin safety applies fully (gloves, ventilation, wash + cure).
• Flexible parts are harder to support: orient to minimize peel forces; thicker supports than rigid resin.

Brand/support reality

• Siraya Tech: the hobby flexible-resin standard; Tenacious is the most-blended resin in the hobby (compatibility with other 405 nm resins is its superpower); direct + Amazon + resellers; strong FB community (13k users, prior pass).
• Formlabs: the pro elastomer (Flexible 50A) — validated, repeatable, 3–5× the price; locked to Formlabs printers; business-grade support.

Community verdict

Tenacious is the community's "fix my brittle prints" additive — the 10–20% blend trick is the single most-repeated resin tip in hobby forums. As a standalone print material, Tenacious 65D is firm-flex (think tough living-hinge), while Flex Black 70A is genuinely rubbery. Formlabs Flexible 50A is the pick when a wearable/prototype must survive repeated flex cycles without tearing. Print-cold failures are the #1 beginner trap with all flexible resins.

Pricing — observed 2026-09-20 (per liter/kg as listed)

Sources consulted

• Google web search 2026-09-20: siraya.tech sales page + engineering-resin collection; woodartsupply.com Tenacious Flex Black 1 kg ($69.99, fresh); Amazon Tenacious Flex Black (stale 278-day crawl); dynamism.com Formlabs Flexible 50A/BioMed Flex 50A (1-day crawl); solidprint3d.co.uk 2022 UK pricelist (stale).
• Facebook groups: zero relevant posts (2026-09-20 pass).
• Reddit/forums/YouTube: Tenacious blend trick widely documented in hobby lore; no new thread pulled this pass (coverage gap, recorded).

Image notes

• ../../images/flexible-resins-01.jpg — Formlabs flexible resin printed parts (formlabs.com engineering resins blog).
• ../../images/flexible-resins-02.jpg — elastomer 3D printed parts illustration (3dadept).
• ../../images/flexible-resins-03.jpg — Figure 4 Rubber BLK 10 manifold adapter part (bechtle-am). All decoded via PIL, converted to RGB JPEG (quality 88), verified non-corrupt. Note: images are category-illustrative (no exact Siraya bottle shot verified); noted.

Open questions / UNVERIFIED

• Siraya Tech bottle sizes behind "from" pricing on sale/collection pages — UNVERIFIED (per-kg normalization impossible).
• Official TDS tensile/elongation for Tenacious 65D and Flex Black 70A — UNVERIFIED in this pass.
• Optimal blend ratios for Tenacious in third-party resins beyond the 10–20% rule of thumb — UNVERIFIED.

Deepening pass (2026-09-20)

Social pulse (Facebook first)

• Failed source, substituted: keyword queries for flexible-resin/Tenacious returned zero posts in the Engineering Filament Lab and the general "3D Printing" group (2026-09-20). Substituted with hobby forums, retailer reviews, and a maker materials table — the Tenacious blend trick is documented extensively in hobby lore even if Facebook stayed silent.

Forums / retailer reviews (Siraya Tech Tenacious — the reference resin)

• Retailer reviews (desertcart/Amazon threads, 2026-09-20): Tenacious is flexible only when printed thin — below about 1/4 inch the print stays flexible after curing; thicker sections read as firm-flex. It takes detail less well than rigid resins, and cleanup is famously messy — described as "motor oil mixed with honey," slippery and sticky at once, thicker than most resins. One reviewer reported a bottle that printed extremely brittle "like ABS" and suspected a wrong-bottle factory batch — a single anecdote, but a reminder to sanity-check a fresh bottle with a test print.
• Print-in-place warning: one owner found that print-in-place articulated models (octopus, shark) break at the joints within a few bends in Tenacious — repeated flex at thin hinges is the failure case. Gaskets and bumpers: yes. Living hinges that cycle thousands of times: expect fatigue.
• The blender trick, quantified: owners report 3–4 parts tough resin to 1 part Tenacious, or ~20–30% Tenacious in standard resin, to toughen brittle prints while keeping detail. Tradeoffs: prints come out slightly less sharp, and once Tenacious is in the mix, parts stay sticky after cleaning unless washed with IPA 99 — Simple Green-style cleaners stop working. One owner found the mix made self-tapping screws hold where plain resin chipped — a genuine functional win.
• Aging caveat (intofpv forum): one long-term user found Tenacious-blend prints get harder and more brittle over time — fine for prototyping, a deal-breaker for parts that must stay flexible for years. Attribute as one user's experience; it matches the general UV-aging behavior of photopolymers.

Maker materials table (openhear hearing-aid project, fresh)

• A 2026 maker materials survey priced the flexible-resin landscape: Formlabs BioMed Flex 80A £200/L (80A, biocompatible, Form 3B+/4B-locked), Formlabs Elastic 50A £200/L (50A, very soft, skin-like), Formlabs Flexible 80A £180/L (non-BioMed prototyping), 3Dresyns OTO-F1 Flex €140/500 mL (60A, works on open printers), Resione F69 Bio ~£50/500 mL (50A–70A tunable by cure time, budget pick), and Siraya Tech Tenacious £50/500 mL (80A, "mix with rigid resin 20:80 for toughened shells; full flexible at 100%"). The price ladder is steep: open-printer elastomers run £50–140 per half-liter; the Formlabs ecosystem runs £180–200 per liter on locked hardware.
• Cost-vs-TPU note (intofpv): for functional flexible parts where resin detail isn't needed, owners point out TPU filament is the cheaper route — flexible resin earns its keep on detail and surface finish, not on price per part.

Failure modes and fixes (new this pass)

• Printed cold: Siraya's ≥25 °C ambient guidance is the #1 beginner trap — cold resin fails; warm the room or enclose the printer.
• Hollowed flexible prints: do not hollow Tenacious-class resins — the outer shell can collapse. Print solid or redesign.
• Joint fatigue: thin flexing hinges break within a few bends — design flex as distributed bending in thin sections, not as pin joints.
• Sticky post-wash: budget IPA 99 for Tenacious blends; gentler cleaners leave residue.
• Wrong-bottle sanity check: test-print every new bottle; if a "flexible" resin prints like ABS, suspect the bottle before your settings.

Price verification (2026-09-20, dated)

• Restated from this file's dated table: Tenacious 65D from $44.85 sale / $65.00 list (siraya.tech; bottle size UNVERIFIED); Flex Black 70A from $32.49/$49.99, 1 kg $69.99 (WoodArtSupply); Formlabs Flexible 50A $219/kg (Dynamism).
• New: open-printer elastomer ladder £50–140/500 mL (Resione/3Dresyns/Tenacious) vs Formlabs £180–200/L — from the 2026 maker table above.

Deepening pass 3 (2026-09-21)

New evidence (public search, observed 2026-09-21; no Facebook signal — keyword endpoint still empty):

• Fresh guide "Best Flexible Resin 2026" (3dprinting.com, published ~31 days earlier, crawled ~1 hour earlier): soft resins need gentle supports, thicker walls, and restrained post-cure because excess UV stiffens them quickly. Comparison prices: Tenacious 65D ~$40/L, Tenacious Flex 70A ~$45/L, Siraya Rebound 55A ~$55/L (new 2026 entry), Formlabs Flexible 80A V2 ~$199/L, YOUSU Flexible 80A ~$30/L. Tenacious elongation quoted at ~70% (matches Siraya's own user guide EAB 70% — resolves the pass-2 UNVERIFIED flag on that figure).
• Reseller review corpus (Siraya Tenacious): recurring ~15% Tenacious as toughness additive in other resins; multiple owners report overexposure makes supports hard to remove; multiple owners note cured Tenacious is firm/tough rather than rubbery (reinforces "firm-flex additive, not rubber replacement"). Aggregate rating 4.7/5 across ~1,090 reviews.
• Tenacious Easy (blue variant): 3.9/5 across 11 reviews; one more owner reported the wrong-bottle/mislabeled-lid batch problem (corroborates the pass-2 bottle anomaly).
• ratebud: ~1,495 reviews analyzed, Grade A; themes "flexible durable easy to print."

Pricing dated 2026-09-21: no fresh changes found; previous per-brand prices stand.

Persistent gaps: independent elongation/tear data on Tenacious Flex 70A; long-term UV-aging data; no Facebook-group owner data.