Clear Resin (Transparent Photopolymer)

Clear resin is an unpigmented, acrylate-based photopolymer for vat photopolymerization: SLA with a laser, DLP with a projector, and MSLA, where a masking LCD screen exposes each layer. Cured clear resin is hard, stiff and glass-like, with mechanical properties close to standard resin. As printed, however, it is translucent rather than transparent: layer lines, support marks and a slightly rough surface scatter light. Optical clarity is therefore mainly a result of finishing.

Choose clear resin when a complex part must let you see inside or let light through: flow and fluidic models, see-through housings, light covers and concept models of transparent products. Plan for its limits from the start. Only faces that can be sanded and polished, or coated, become close to transparent; internal channels stay frosted. All clear resins carry a slight yellow tint that grows with UV exposure, heat and age, and the material is as brittle as standard resin. Through Uretyco's partner network, clear resin is offered for SLA, DLP and MSLA printing; process and finishing are confirmed during quote and order review.

Mechanical and physical properties

Printing clear resin with SLA, DLP and MSLA

Clear resin prints like standard resin: layer by layer, usually hanging from the build platform, followed by washing, support removal and UV post-cure. Clarity, however, starts at the printer. Orientation decides where supports and layer steps fall, and washing and curing decide how hazy or yellow the part becomes. Design and ordering points:

• Viewing faces: decide which faces must be transparent and keep supports off them. Flat and convex faces are the easiest to sand and polish; concave areas, recesses and fine textures are hard to reach.
• Internal channels and cavities: they cannot be polished, so they stay translucent. Keep channels as large and straight as the design allows, with openings for flushing out uncured resin. Flushing a channel with clear resin or lacquer and curing it can improve internal clarity, at extra cost.
• Wall thickness: thin, even walls look clearer and less yellow than thick solid sections, which show more tint and can hold internal stress. Avoid abrupt changes in thickness in visible areas.
• Washing and drying: long soaks in solvent and incomplete drying cloud the surface, which is why clear parts need a controlled wash and complete drying before post-cure.
• Post-cure: a full post-cure gives the rated strength but deepens the yellow tint. When appearance matters more than strength, say so in the order notes so the cure can be balanced accordingly.
• SLA, DLP or MSLA: all three print clear parts. SLA suits larger parts, while DLP and MSLA are efficient for batches of small parts. Final clarity depends more on finishing than on the process.

Tolerances and surface

Without a drawing tolerance, Uretyco applies the SLA default of ±0.2 mm or ±0.2%, whichever is greater; actual results vary with technology, orientation, part size, supports and post-processing, and fit-critical features should be tested before production. Sanding and polishing remove material and round edges slightly, and a clear coat adds a thin layer, so mark fit-critical faces that must stay unfinished. Large flat windows are the hardest case: post-cure distortion and layer steps show clearly in transparent parts.

Finishing options

For clear resin, finishing decides the result. Specify the clarity you need face by face, because polishing every surface costs far more than polishing a single window. Typical options:

Cost and lead-time drivers

Printing clear resin costs about the same as standard resin; finishing labor makes the difference:

• Number and size of clear faces: every face that must be transparent is sanded and polished by hand, so cost grows with area and with how hard the face is to reach.
• Geometry: recesses, ribs and internal corners slow finishing down; smooth, open shapes are faster.
• Coatings: sprayed and dipped coats need drying or curing time, which adds to lead time.
• Orientation and supports: build height drives print time, and keeping supports away from viewing faces can require a less efficient orientation.
• Cosmetic requirements: small flaws that stay invisible in opaque resin show in clear parts, so state the cosmetic standard for viewing faces.

Clear resin vs. other transparent options

Clear resin is the practical route to transparent parts with internal features or complex shapes that cannot be machined. When the part is a lens, light guide or window with simple geometry, machined PMMA or PC gives better and more consistent clarity. For tens of identical clear parts, clear polyurethane cast in silicone molds from a polished master can be more economical than finishing every print.

When not to choose clear resin

Typical applications

• Flow-visualization and fluidic models, manifolds and transparent test fixtures.
• See-through housings and covers that show internal mechanisms.
• Light covers, light pipe prototypes and lighting concept models.
• Concept models of bottles, caps, cosmetic packaging and other transparent products.
• Display, presentation and art pieces.
• Anatomical and teaching models in which inner structures must be visible.

Specifying clear resin on Uretyco

1. 1
   Upload STL, 3MF or STEP

   Use a fine mesh so curved faces stay smooth, and check that channels have openings for washing and flushing.

2. 2
   Select clear resin and the process

   SLA, DLP or MSLA; unless part size or batch quantity points to one of them, let the quote compare them.

3. 3
   Define clarity face by face

   Use a marked-up image or drawing to show which faces must be transparent, which may stay translucent and which can be frosted.

4. 4
   Choose finishing

   Polishing, clear coat, UV-resistant coat or as printed; note any tint and any fit-critical faces that must stay unfinished.

5. 5
   State the use conditions

   Light exposure, temperature and contact with fluids or cleaners help the partner confirm suitability during quote and order review.

FAQ

Can a printed clear part be as clear as glass or PMMA?

On accessible flat or convex faces, careful sanding and polishing or a good clear coat come close. The part as a whole is less consistent: internal faces stay frosted, thick sections look slightly yellow, and small inclusions or layer marks can remain. For lenses, light guides and windows, machined PMMA is the reliable route.

Why do clear resin parts turn yellow?

The photoinitiators that make the resin cure leave a slight yellow tint, and UV light, heat and time deepen it. Thick sections and heavily post-cured parts show it most. A controlled post-cure, a UV-resistant clear coat and storage away from sunlight slow the effect but do not stop it.

Can internal channels be made transparent?

Not by polishing, because the surfaces cannot be reached. Flushing the channel with clear resin or lacquer and curing it improves clarity to some extent. Where a view into the channel is essential, splitting the part into two halves with polished faces and joining them with a clear adhesive gives the best result.

Can clear resin parts carry water or other fluids?

For flow tests and models, water and many water-based fluids are fine for limited periods. Cured resin slowly absorbs some water and can turn hazy, and prolonged contact with alcohols, solvents and some cleaners can swell or craze the surface. State the fluid, temperature and duration so suitability can be checked; for long-term fluid contact, PMMA, PC or a resin grade intended for it is often the better choice.

Related resources

• PMMA (Acrylic)Machined parts with optical clarity.
• Polycarbonate (PC)Tough, transparent parts for impact loads.
• PolyJet ClearTransparent jetted photopolymer that can be combined with color.
• Standard SLA ResinOpaque general-purpose resin for cosmetic models.
• Cast PolyurethaneClear castings from polished master patterns.
• Surface FinishingHow finishing affects appearance, cost and delivery.