Somos WaterClear

How a water-clear resin actually behaves

Clarity in stereolithography is a property of the route, not only of the resin. A part comes off the machine with uncured resin on its surfaces, and that film scatters light, so a freshly printed part usually reads milkier than the same part after it has been cleaned, sanded and polished. Two parts printed from the same bottle can therefore differ noticeably in appearance if they were finished differently.

Water-clear grades exist because earlier clear photopolymers absorbed moisture and clouded, or crazed, when they sat near fluids or in humid air. The formulation resists that change so clarity holds up in service rather than only on the day of delivery. Clear photopolymer does still drift towards a warmer, yellower tone under prolonged ultraviolet exposure, so where a part is going outdoors or under strong lighting for months at a time it is worth stating that up front — it changes the advice on coating.

Designing and building for clarity

• Layer orientation against the optical face. The clearest faces are the ones parallel to the build layers. On a face that cuts across the layer stack, each layer edge is a step that has to be polished away, and every step is a place light scatters.
• Where the supports sit. Supports leave witness marks. Placing them on a non-optical face keeps the polishing work off the surfaces you actually need clear.
• Section thickness. Thicker clear sections take longer to clean and to sand back to an even finish. Very thin walls can polish through, so the target clarity and the wall thickness have to be considered together.
• Sanding and polishing is a graded sequence. Clarity comes from stepping through progressively finer abrasives and then polishing, not from a single operation. Deeper steps need more material removed, which is why a coarse as-printed surface costs more finishing time than a fine one.
• Clear coating changes more than appearance. A lacquer or clear coat lifts apparent clarity quickly, but it also becomes the surface that takes handling and wear, and it carries its own ultraviolet behaviour. Treat it as a design decision, not a cosmetic afterthought.

When it is the right choice — and when it is not

Water-clear resin suits parts whose job is to be seen through or to move light: flow-visualisation models, light pipes and guides, lens and sensor housings, packaging mock-ups, and display models where internal features have to be visible. In those cases the benefit is that a single printed part replaces a tooling investment that would only be justified at volume.

It is the wrong choice where the part has to survive impact, hold tight tolerance as a functioning component, or meet a defined optical specification. Where light has to be transmitted or shaped to a stated figure, or transmission has to be characterised across a spectrum, the part belongs on a machined or moulded optical route instead. For visual certainty alone, standard clear or tinted SLA resins are usually sufficient; for toughness without a transparency requirement, an ABS-like resin or SLS nylon is a better match.

What to send for a quotation

• The 3D model, ideally in STEP or STL
• Which surfaces have to be clear, and which can be left as-printed
• Whether clarity is optical — light is transmitted or shaped — or simply visual
• The finish target: as-printed, sanded, polished, or clear-coated
• Wall thickness through the clear section
• Whether it is a one-off display piece or the first of a repeat batch
• Whether the part will see ultraviolet, humidity or elevated temperature in service
• Any thread, insert or mating feature that must still hold tolerance after finishing

Send the model through the RFQ form and an engineer will confirm the print orientation, the finishing route and the lead time in writing before anything is quoted.