For 3D printing, an isopropyl alcohol percentage of 90% or higher works reliably, especially when washing uncured resin off SLA/DLP prints. A 70% solution contains too much water, which slows the dissolution of uncured resin and leaves a sticky film on the finished part.
The correct isopropyl alcohol percentage for 3D printing
When you pull a print out of a resin vat, it is coated in a layer of liquid photopolymer that must be removed before curing. Isopropyl alcohol (IPA) dissolves this uncured resin because both are non-polar solvents. The concentration of the IPA determines how effectively it can do this. A 90% or 99% concentration has very little water, so it aggressively breaks down the resin and carries it away from the surface. In contrast, a 70% solution is 30% water, and that water acts as a barrier. It dilutes the solvent power, meaning you need longer soak times and more agitation to get the same result. In practice, 70% IPA often leaves a hazy residue on the print that only shows up after UV curing, ruining the surface finish. For consistent, clean results, buy 99% isopropyl alcohol and store it in a sealed container to prevent it from absorbing moisture from the air.
Special cases: Biocompatible and engineering resins
If you are working with certified biocompatible materials, such as Formlabs' Dental SG or BioMed Clear, the cleaning requirements are stricter than standard resin. Formlabs explicitly requires IPA with a concentration of 96% or higher for washing biocompatible resins. This ensures that no water-soluble contaminants remain on the surface and that the part is sufficiently clean for medical or dental use. Using a lower percentage may leave trace amounts of resin or cleaning residue, which can cause cytotoxicity when the part contacts living tissue. For engineering resins like Tough or Rigid, a 90%+ IPA wash is still the baseline, but you should check the technical datasheet for any specific solvent restrictions, some high-temperature resins may require a secondary rinse in fresh IPA to achieve full mechanical properties.
How to wash resin prints with isopropyl alcohol
Washing resin prints is a straightforward process, but the method matters more than most people think. Follow these steps to get a clean, fully cured part without damaging it.
Step 1: Prepare your wash station
Fill a container with 90% or higher IPA. The container should be large enough to fully submerge the print with room to spare. A metal or glass container is best, some plastics can degrade or warp when exposed to IPA for long periods. Place the container in a well-ventilated area, away from any open flames or sparks.
Step 2: Submerge and agitate
Lower the print into the IPA bath. Gently swirl the container or use a soft brush to agitate the liquid. This mechanical action helps dislodge uncured resin from crevices and intricate details. Do not shake vigorously, this can cause the print to knock against the container walls and break delicate features. For most parts, 3 to 5 minutes of gentle agitation is sufficient. For complex models with deep channels, you may need 10 minutes or more.
Step 3: Rinse in fresh IPA
After the initial bath, move the print to a second container of clean IPA. This rinse removes any resin-laden alcohol that is still clinging to the surface. Swish the print for 30 seconds to a minute. If you skip this step, you risk leaving a thin film of dissolved resin that will cure into a dull, sticky layer.
Step 4: Air-dry before UV curing
Set the rinsed print on a clean, lint-free cloth or paper towel. Let it air-dry completely, this usually takes 5 to 10 minutes. The IPA must evaporate fully before you cure the part under UV light. If any alcohol remains, it can trap uncured resin beneath the surface, causing blotchy curing and reduced strength. Once dry, cure the print according to your resin manufacturer's recommended time and wavelength.
Throughout this process, wear nitrile gloves and safety goggles. IPA can dry out your skin, and uncured resin is a skin sensitizer. Work in a ventilated space to avoid inhaling alcohol vapors.
When to replace your IPA wash bath
Your IPA bath does not last forever. As you wash prints, the dissolved resin accumulates in the alcohol, reducing its cleaning power. You can measure this contamination with a simple hydrometer. The hydrometer reads the specific gravity of the liquid, as resin concentration rises, the density of the IPA increases. When the resin concentration in your wash bath reaches 10-12%, it is time to replace the IPA. At this point, the alcohol is too saturated to dissolve more resin effectively, and prints will come out with a sticky residue. To test, pour some of the used IPA into a clean cylinder and float the hydrometer. If the reading indicates 10-12% resin by weight, discard the old IPA into a hazardous waste container and refill with fresh solvent. Do not pour used IPA down the drain, it contains uncured photopolymer that is toxic to aquatic life.
Water-washable resins: An alternative to IPA
Not every resin requires isopropyl alcohol. Water-washable resins are formulated with a different chemistry that allows them to be cleaned with plain tap water. These resins contain hydrophilic components that dissolve in water, so you can simply rinse prints under running water or soak them in a water bath. Using IPA on water-washable resins is unnecessary and can actually damage the part. The alcohol can cause the partially cured resin to swell or become brittle, and it may strip away surface detail that water would preserve. For these materials, stick to water, it is cheaper, safer, and produces identical results. Just be aware that water-washable resins still require UV curing, and the water used for cleaning should be disposed of properly, as it contains uncured resin particles.
Using isopropyl alcohol to clean FDM prints
For FDM (fused deposition modeling) prints, IPA has a more limited role. It is safe to use on PLA to remove bed adhesion residue, fingerprints, and light grease from the surface. A quick wipe with a cloth dampened with 99% IPA will clean the print without attacking the plastic. However, IPA is often ineffective on ABS and PETG. These materials are more chemically resistant, so IPA cannot dissolve the stubborn blobs, stringing, or support material that often sticks to them. Acetone is a better solvent for ABS, but it can melt the plastic if used carelessly. For PETG, a warm soapy water bath is usually more effective. The primary application of IPA remains resin printing, for FDM, it is a surface cleaner, not a solvent for removing failed extrusion.
Safety precautions and ventilation
Isopropyl alcohol is highly flammable, and its vapors can form explosive mixtures in air. Always use IPA in a well-ventilated area, ideally near an open window or under a fume hood. Keep it away from any ignition source, no smoking, no pilot lights, no sparking electronics. Store the bottle tightly sealed when not in use, and never leave an open container unattended. Wear nitrile or neoprene gloves to protect your hands, and safety goggles to shield your eyes from splashes. During the UV curing step, the same ventilation rules apply, as residual alcohol on the print will evaporate as the part heats up. Dispose of used IPA and resin-contaminated paper towels as hazardous waste, not in your regular trash or recycling bin.
