How to make and maintain less brittle prints


I’ve had my formlabs 1+ for a few weeks now, and have been trying out all the different resins. I’ve been doing some design work in Rhino 3D and I thought it would be cool to print myself a pair of eyeglasses, and get my local optician to make up the lenses.

My test print was in black, and came out pretty well. I soaked it for about 20 minutes in the IPA and then cured in a UV oven for a few hours before cleaning. The result came out really nice, but when I started stress testing the print by bending the legs - snap! At first, the print seemed to have the flexibility I needed, but it was like it was brittle at the core.

Recent topics I’ve read have suggested a shorter soak in IPA, covering the green parts in uv blocking polyurethane, mixing the flexible resin in with your desired color resin, and using a 3rd party resin, like MadeSolid. I’m in the process, right now, of trying the first 2 - I’m printing a number of legs, and I’m going to give them different soak and cure times, and try uv blocking at various stages. However, I wonder if anyone has tried and succeeded with the kind of project I’m attempting?

So whichever resin or resin mix you use, the two main things that cause brittleness are exposure to IPA, and exposure to UV light. Your previous method had way to much exposure to both. I try to keep my IPA exposure to 2-3 minutes max, I really want to switch to a sonic cleaner with water to avoid the IPA all together. Next is the UV exposure you only want to cure long enough to get rid of the tackiness of the surface. Once you get to this point it is important to seal the part with some kind of UV blocker. If you don’t do this last step exposure to regular daylight will slowly continue to expose the part making it more brittle over time.

As for resin mixes, and alternative resins, there is definitly a large amount of variabilty from one to another when it comes to durability, however they will all do much more poorly if you don’t follow the advice in the first paragraph.

I hope this helps.


It really does, thanks. I found the same myself with my test prints right now. One got a 2 min IPA bath, the other got 10 mins. Both then got 1 hour in the UV oven. They came out nice and flexible - really exactly what I wanted. I then left them both out in the sun for a few hours - one fell off the table and smashed - the other broke in my hand like peanut brittle.

Time to order some uv blocker!

This has worked well for me, there is also a gloss version. If there’s a better one out there let me know!

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Also, using a soft brush during the IPA rinse can help reduce the overall soaking time required

Thanks, guys. i appreciate the info. Testing of my prints is going slower than I had hoped - a pesky thing called ‘work’ keeps on getting in the way :slight_smile:

I have the Krylon stuff ready to go, as well as some Plasti-Kote (which claims to be UV resistant, but is kind of vague on the details). Test prints are drying on my bench now. Polyurethane does offer some physical protection, but my clear prints are already yellowing slightly.

As for materials, I sent an email to formlabs, and they inform me that their resin isn’t suitable for what I want to do (won’t be robust enough). However, I emailed the people at, and received an email from their CEO. Their Vorex resin is the strongest on the market, but however only comes in black and a non-attractive orange. One of the prints drying on my bench is the black Vorex. Early days, but I can tell you it felt different right off the build plate. It is definitely more flexible than the formlabs black. I’ll be testing its strength with and without the UV and polyurethane coatings. If this post is still open when I’m done, I’ll post results.

I would love to hear results on the vorex - I was hoping to make a prosthetic hand model with the formlabs resin but it wasn’t nearly strong enough. Was looking at vorex but didn’t want to drop the money if it wasn’t going to work.

+1 for vorex. Have printed identical parts in Vorex and Formlabs and dropped both (accidentally). The Formlabs broke into 3 pieces, while the vorex was unaffected. The vorex bends more, so it doesnt break. You should be aware that the vorex probably loses 5-10% detail/clarity compared to the FormLabs resin - it just doesn’t do overhangs as well.

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