Water-washable resin is an acrylate photopolymer for MSLA and DLP printers. It contains water-compatible components, so uncured resin can be rinsed off printed parts with water instead of isopropyl alcohol (IPA) or other solvents. Printing, support removal and UV post-cure work as with standard resin, and detail and surface quality are similar. What changes is the cleaning step and, to some extent, how the cured part behaves.
Choose water-washable resin for visual models, miniatures, figurines and quick form studies where fine detail matters and mechanical demands are low. Its limits are worth knowing in advance. Cured parts are typically somewhat more brittle than standard resin, absorb more moisture and can crack days after printing, especially when they are hollow or over-cured. The name also invites a misunderstanding: the water used for washing contains dissolved uncured resin and must be handled as chemical waste, not poured down the drain. Through Uretyco's partner network, water-washable resin is offered mainly for MSLA and also for DLP; suitability is confirmed during quote and order review.
Mechanical and physical properties
| Property | Typical value | Notes |
|---|---|---|
| Tensile strength | ≈ 25–50 MPa | Fully post-cured; brand-dependent and often slightly below standard resin. |
| Elongation at break | ≈ 5–15% | Varies widely between brands; fine features break easily. |
| Tensile modulus | ≈ 1.5–2.5 GPa | Often not stated on datasheets; similar to standard resin. |
| Impact resistance | Low | Similar to or below standard resin; few datasheets give an Izod value. |
| Hardness | ≈ 75–85 Shore D | Hard surface after full post-cure. |
| Heat deflection temperature | ≈ 45–60 °C | Where stated; many consumer-grade datasheets do not report it. |
| Density | ≈ 1.1–1.2 g/cm³ | Cured resin. |
| Moisture sensitivity | Higher than standard resin | Parts absorb water over time and can soften, swell slightly or crack in humid conditions. |
| Delayed cracking | Known risk | Mainly in hollow, thick or over-cured parts and where water was trapped before curing. |
| UV stability | Poor | Yellows and embrittles in sunlight. |
Typical values for fully post-cured water-washable resins. Datasheets in this class are often incomplete, test methods are not always stated, and formulations differ considerably between brands. Treat the values as orientation only and validate parts that must carry load or stay dimensionally stable over time.
Printing and washing with MSLA and DLP
Water-washable resin prints on standard MSLA and DLP machines with the same orientation, support and hollowing rules as other resins. Because the cured material reacts more strongly to trapped water and over-curing, a few design points matter more than usual:
- Orientation and supports: parts are usually tilted to reduce peel forces, with supports on hidden faces. Mark cosmetic faces so support marks stay off them.
- Hollow parts: hollowing saves resin, but hollow shells are the most crack-prone. Use generous drain holes, at least two, and walls of about 2 mm or more, so resin and water can escape and the shell is strong enough.
- Thick solid sections: very thick, solid volumes build up internal stress during curing; hollowing with proper drainage, or a lighter and more even design, reduces the risk.
- Thin features: fine details print well, but slender pins and thin walls break easily; keep them short and supported.
- Fits and threads: plan clearances and test fit-critical features; use inserts or post-machining for threads that carry load, in line with Uretyco's 3D printing guidance.
Washing and waste handling
Uncured resin is removed with water, usually by a short rinse with agitation in a wash station or ultrasonic bath, followed by a rinse in clean water. The part must then dry completely before UV post-cure: water left on the surface or trapped inside causes white marks and can crack the part during or after curing. Washing and waste handling are carried out by the manufacturing partner; the points below matter mainly if your team also cleans or reworks parts in house:
- Wash time: short rinses are enough; long soaking lets the part absorb water and raises the risk of cracking.
- Drying: dry parts completely before post-cure, with compressed air or enough time; hollow parts take longer.
- Wash water: it contains dissolved uncured resin, which is harmful to aquatic life. Do not pour it into a sink or drain.
- Treatment: a common practice is to expose the water to UV light or sunlight until the dissolved resin has cured, filter out the solids and dispose of both according to local waste rules.
- Safety: uncured water-washable resin can irritate and sensitize the skin like any other resin. Wear nitrile gloves and eye protection when handling it.
The name describes the cleaning method, not the waste. Rinse water, used filters and uncured resin residues remain chemical waste and must be handled under local rules. The same applies to the IPA used with standard resins.
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. Water-washable parts can also change slightly over time as they absorb moisture, so do not rely on them for tight fits that must hold for months. Surfaces are as smooth and detailed as those of standard resin printed on the same machine.
Finishing options
Water-washable parts are finished like standard resin. Sealing the surface is especially worthwhile here, because it slows moisture uptake and UV aging. Typical options:
| Finish | Effect | Notes |
|---|---|---|
| Supports removed, lightly sanded | Lowest cost | Small nubs remain where supports attached. |
| Fully sanded | Uniform surface | Dry sanding is preferred; after wet sanding, dry the part completely. |
| Primed and painted | Color, sealed surface, UV protection | Recommended for parts that are kept; slows moisture uptake and yellowing. |
| Clear coat | Sealed surface without color change | Protects natural-color parts and miniatures. |
For display models, miniatures and reference samples, a primer and paint or a clear coat noticeably extends service life, because it limits moisture uptake and UV exposure. State it in the order if the parts are meant to last.
Cost and lead-time drivers
Water-washable resin is priced like other MSLA resins; washing with water does not make parts noticeably cheaper:
- Resin and volume: material cost is similar to standard MSLA resin, so part volume and hollowing drive it.
- Batching and height: MSLA cures a whole layer at once, so print time depends on build height and many small parts can share one build.
- Drying time: parts must dry completely before post-cure, which adds hours for hollow or complex parts.
- Finishing: sanding, priming and painting are manual and often the largest cost on cosmetic parts.
- Availability: offered by partners with MSLA and DLP capacity; feasibility and lead time are confirmed during quote and order review.
Water-washable resin vs. other options
| Material and process | Cleaning | Toughness | Moisture sensitivity | Best for |
|---|---|---|---|---|
| Water-washable resin (MSLA, DLP) | Water | Low; brittle | Higher | Visual models, miniatures, quick form studies |
| Standard resin (SLA, DLP, MSLA) | IPA or another solvent | Low; brittle | Low | Cosmetic models, master patterns |
| ABS-like resin (MSLA, SLA, DLP) | IPA or another solvent | Moderate | Low | Detailed prototypes that are handled and assembled |
| PLA (FDM) | No washing | Low; brittle | Low | Low-cost visual prototypes with visible layers |
Water-washable versions of ABS-like and other resins also exist; they share the cleaning advantage and the moisture caveats. When a part must be robust, is handled often or has to last, a solvent-washed standard or ABS-like resin is usually the better choice.
When not to choose water-washable resin
Load-bearing, impact-loaded or snap-fit parts: use ABS-like or tough resin, or PA12. Parts used in water, in high humidity or outdoors: water-washable resin absorbs moisture, yellows and embrittles. Hollow display pieces with small openings that cannot drain or dry completely. Archive or reference models that must stay free of cracks for years without sealing. Temperatures above about 45–55 °C. Skin-contact, medical or food-contact use: suitability depends on a certified grade, validated processing and your own regulatory assessment, and water-washable resins are not intended for it.
Typical applications
- Visual and concept models for design reviews.
- Miniatures, figurines and tabletop models.
- Architectural and presentation models with fine detail.
- Quick form studies and design iterations.
- Small decorative parts that will be primed and painted.
- Teaching and demonstration models used indoors.
Specifying water-washable resin on Uretyco
- 1Upload STL, 3MF or STEP
Use a fine mesh so curved surfaces stay smooth, and check units and scale.
- 2Select water-washable resin and a color
Or describe the use and let the quote compare it with standard or ABS-like resin.
- 3Plan hollow parts
State whether parts may be hollowed and where drain holes are acceptable; keep shell walls at about 2 mm or more.
- 4Mark cosmetic faces
So supports go on hidden faces; add notes for fit-critical features.
- 5Choose finishing
As printed, sanded, primed and painted, or clear coated; sealing is recommended for parts that are kept.
FAQ
Can the wash water go down the drain?
No. The water contains dissolved uncured resin, which is harmful to aquatic life. A common approach is to cure the dissolved resin with UV light or sunlight, filter out the solids and dispose of them and the water according to local waste rules. Parts ordered through Uretyco are delivered washed and post-cured.
Is water-washable resin weaker than standard resin?
Often slightly, although it depends on the brand. Many grades are a little more brittle and absorb more moisture, and some are prone to delayed cracking. For models and prototypes the difference rarely matters; for parts that are handled a lot or kept for years, standard or ABS-like resin is the safer choice.
Why do water-washable parts sometimes crack after a few days?
The usual causes are water trapped in hollow sections or pores before curing, over-curing that leaves the resin brittle, and internal stress in thick or unevenly thick sections. Short washes, thorough drying, a measured post-cure, adequate drain holes and sealing the finished part reduce the risk.
Is water-washable resin safer to handle?
It removes solvent from the cleaning step, which helps with fumes and flammability. The uncured resin itself is still a skin and eye irritant and can cause sensitization, so it needs the same gloves, eye protection and ventilation as other resins.
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