Resin printing and toxicity – keeping printing safe for you and your environment

Resin printing is still an emerging technology that is becoming increasingly popular to print miniatures and decorative items, due to it’s ability to reproduce fine detail at a price point that is reasonable to the hobbyist. UV light cures resin on a build plate which builds up a complete model. Specialist resins also allow for rubberised items, castable prototypes and (at a high cost) low shrinkage high-quality dental models. The major downside of printing with resin is the resin itself, which is toxic to touch and produces strong fumes. Though the level of fumes varies between resins, none can be classed as completely safe.

Safety equipment for printing

Resin fumes

I’m particularly sensitive to resin. Not to touch (I’ve touched accidently either by handling uncured models when I first started, or from breaks in protective gloves where resin soaked IPA seeps in), but I react if I inhale resin fumes I quickly end up with a swollen throat.

We first started with the printer in it’s own room with an open window but the smell of fumes was significant outside of the room and I’d have a reaction. I’ve found that the suitable amount of fume protection is:

  • Resin printer in it’s own room, garage or grow tent. You can’t have your printer sitting in a communal area, bedroom or office. A grow tent or other enclosure may make this a possibility but the fumes must be removed via an extractor fan, otherwise they’ll just build up and spill out when you open the enclosure.
  • Extractor fan blowing air outside. This is necessary to actually remove the fumes from the building, otherwise you’re just blowing them around. Creating negative pressure in the room means that the resin fumes wont seep out into other areas. If you’re in a (heated) shed or garage, you may be happy to have a fume filled room but extra care to use protective facewear when you go inside.
  • Face mask. My printer came with a simple cloth mask that really isn’t appropriate. You need an appropriate respirator mask to deal with VOCs

Please protect yourself from fumes and take care not to inflict those on the people or pets you live with.

An aside: I’m disappointed in the lack of safety information on the resin itself. If this were a paint, glue or epoxy it would be covered in safety warnings and guidance. My resin bottle is blank.

What about carbon filters? Carbon filters reduce smell but do not reduce VOCs to an acceptable level. Please do not rely on these.

Touching resin

Avoid touching resin. That’s about the whole of it. Wear nitrile gloves – either the thin disposable kind or the thicker ‘washing up’ gloves that will affect your dexterity but offer a lot more protection. I’ve had the thin gloves break frequently and resin soaked IPA leak in which really isn’t ideal.

Working with resin gets messy and it can spatter, so be aware of how clean your worksurfaces are and what you touch while all resiny. Gloves should go on when dealing with any part of the process – from adding resin to the printer to curing and removing supports. Your cleaned/cured model (in water or IPA) still has traces of uncured resin on it. The only time I don’t use gloves in the print room is handling the USB and taking cured models out of the curing station.

Making your printed model safe

Your model needs cleaning and curing! Your cleaning liquid (water or IPA/IPA alternatives dependant on resin) will quickly become filled with a suspension of uncured resin so after cleaning it’s not ‘clean’ enough to be non-toxic. Make sure your model is completely dry before curing, otherwise you’ll end up with white bloom and/or delamination on some surfaces.

Properly curing your model not only makes it safe but also prevents splitting of the model in the future. Uncured liquid resin trapped in hollowed prints will eat at the cured resin. It may be 6 months in the future but can result it a ruined print.

Your basic cure should be in the form of an array of UV LEDs (or several hours in sunlight if you have clement weather). Most of the printer manufacturers produce a machine to cure or clean/cure combo. I use an Elegeoo Mercury Plus Wash + Cure machine which makes the process quite simple but is already too small for a number of my prints. I also have a set of under counter LED strips to cure larger models and generally cure my work area to keep it safe. The length of time to cure depends on the size and thickness of the model. Over-curing wont damage your model. If you use clear resin over-curing may result in slight yellowing.

Many models are hollowed out to reduce the amount of resin needed for print. It’s important that if you hollow out a model that there are at least two drainage holes in the model. This is to allow air to enter and assist drainage (just like trying to empty a bottle with/without that trick with the straw which if you’re as old as I am you learned doing strawpedos). Beware of resin traps if the hollowed section doesn’t make a single area. Miniatures tend not to need hollowing but I find if the interior area is more than an inch wide then it starts needing to be hollowed.

Do not infill, either with or without drainage holes. It’s not necessary and makes properly curing impossible, increasing the risk of retained liquid resin in the model.

A final note on curing – even when completely cured your model is not food safe. Do not use as mouthpieces, drinks receptacles, etc. I’d even be wary using as a plant pot for herbs and would put an inner container for the soil. Water washable resin shouldn’t be used in applications where it would be constantly damp, such as plant pot decorations, as it will eventually react to the water and split.

Disposing of supports, spilt resin and cleaning liquid

A final concern is preventing resin from entering the environment. Uncured resin should not enter the environment in any form. The following are unacceptable:

  • Washing resin from a print under a tap down a drain (this includes water washable or plant derived resins)
  • Washing resin in a container and throwing that water down a drain/onto grass/etc
  • Throwing out anything containing uncured resin into the waste bin

Any water, IPA or other liquid that contains uncured resin should be evaporated off outside. Any uncured resin (from cleaning, failed prints, empty bottles) should be cured before being thrown away. This could be outside in the sun (again, if you’re lucky enough to have good weather), or under UV light. My bin has a UV light above it so everything that goes in gets blasted.

Final word

The results from resin printing can be incredible! No-one wants to gatekeep the hobby but the chemicals that are being used really do need care and attention to not put yourselves and your environment at risk. There’s so much to cover that I’m sure I’ve missed something or could go into more detail but I hope to do so too. Research into risks around resin printing is finally happening after being in the general market so long so it will be good to have some conclusive answers on the effects resin can really have.