Rigid Clear Casting Resin
Rigid Clear is a water-clear, UV-stabilized two-part urethane that cures to a hard, glassy solid of about 80–85 Shore D — close to cast acrylic in stiffness and feel, with light transmission near 90 % through a polished section a few millimetres thick. Cast under vacuum in a silicone mold taken from a polished master, it is the way to get lenses, light guides, windows and see-through housings in prototype and pilot quantities without machining and polishing each one from PMMA or PC.
Popular rigid clear resin grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Best for |
|---|---|---|---|---|---|
| Rigid Clear | 38 | 40 | 1.06 | Good | Cast lenses, light guides, windows, tinted covers |
All 1 rigid clear resin grades
Choose rigid clear resin for
Lenses, indicator windows and light guides in 10–100 pieces; transparent housings and covers that show the mechanism inside; fluidic manifolds and flow cells whose channels must be watched; LED and display bezels; and tinted or smoked versions of an opaque ABS-Like part cast from the same mold.
Look elsewhere when
The window will sit in sunlight for years (even stabilized urethane yellows slowly — machine PMMA or use glass), it must resist scratching or solvents (PMMA, PC or Borofloat 33), optical quality beyond a display window is needed (polished PMMA or optical glass — cast faces carry the mold finish and faint flow marks), it runs above about 70–80 °C (PC), or a single one-off is enough and SLA Clear Resin will do.
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Rigid clear resin by application
- Lenses and light guides
- Rigid Clear cast from a polished master; leave 0.2–0.5 mm on optical faces for polishing, or clear-coat the part to fill the mold texture.
- Transparent housings
- Rigid Clear in walls of 2–4 mm so the resin degasses fully; thick sections trap bubbles and show the faint warm tint of a UV-stabilized urethane.
- Tinted and smoked covers
- Rigid Clear with translucent dye — a few tenths of a percent shifts a clear part to a smoked or coloured lens without losing transparency.
Working with rigid clear resin
- Casting
- The master is polished to the finish the part must have, since every scratch on it appears on every casting; the silicone mold is taken from it and the resin is mixed, vacuum-degassed and poured under vacuum to keep bubbles out of the clear section. Cure at 60–70 °C, then post-cure for full hardness and clarity. Clear grades are harder on molds than pigmented ones — expect 15–25 shots per mold.
- Tolerance and design
- Expect ±0.15 mm on small features and ±0.3 % overall; shrinkage is 0.15–0.3 %. Keep clear walls 2–4 mm and uniform: thick masses read amber and trap bubbles, thin ribs distort. Give lenses generous radii; sharp internal corners show stress whitening under load.
- Finishing
- Fine abrasive and a polishing compound bring a cast face to a glass-like gloss; a UV-stable clear coat or vapour polish fills fine mold texture and protects the surface. Parts can be tinted in the mix, dyed after casting, or masked and back-painted for a two-tone look. Clear urethane bonds with UV-cure acrylic, epoxy and cyanoacrylate adhesives; solvent welding does not work, and there is no plating.
Other polyurethane series
Rigid Clear Casting Resin — frequently asked
What is rigid clear resin?
Rigid Clear is a water-clear, UV-stabilized two-part urethane that cures to a hard, glassy solid of about 80–85 Shore D — close to cast acrylic in stiffness and feel, with light transmission near 90 % through a polished section a few millimetres thick. Cast under vacuum in a silicone mold taken from a polished master, it is the way to get lenses, light guides, windows and see-through housings in prototype and pilot quantities without machining and polishing each one from PMMA or PC.
Which grade of rigid clear resin should I use?
Rigid Clear is the only grade in this group, so the choice is how to use it: neutral for windows and light pipes, tinted with translucent dye for indicator lenses and smoked covers, and cast against a matte mold where a frosted diffuser is wanted. Choose it when several identical clear parts with molded detail, undercuts or inserts are needed; when one flat window is all it takes, a machined and polished PMMA or PC blank is faster and more scratch-resistant.
Will a cast clear urethane lens yellow?
Slowly. UV-stabilized Rigid Clear stays visibly clear indoors for years, but months of direct sun turn it faintly amber and eventually brittle, and thick sections show a slight warm tint from day one. For an outdoor lens machine PMMA, which does not yellow, or specify a UV-blocking clear coat over the casting.
Cast clear urethane or machined acrylic for a window?
Machined and polished PMMA for a flat or simple window, a one-off, or anything that must resist scratching and solvents; it is also the clearer material. Cast Rigid Clear when there are several identical parts with molded detail — snap features, bosses, curved lens faces, inserts — because the mold does the shaping once and each casting comes out ready to polish or coat. Transmission is comparable at 2–3 mm; hardness and scratch resistance favour acrylic.