Mold Release for 3D printed molds

Hi, I’m currently trying to cast some liquid urethane plastic (smooth-cast 305) in a 3D Printed mold, however I’m struggling to find a decent mold release. I’ve tried CRC 808 silicone and mann ease release 200 but neither of these have worked well, as the cured plastic sticks to the mold.

Does anyone have any experience with molding liquid plastics using molds printed with the formlabs resin? If so can you recommend a good mold release?

Any help would me much appreciated.


Hi Elliot,

I do a bit of moulding, I work on the basis that if the final part need to be hard (like resin) then i use a silicon mould, if i want a “rubber” part I use a hard mould.

So in your case i would print the final part as you want it, mould it in silicon and then pour the resin into that mould and extract etc etc.

Hope that makes sense.


If you want to stick with a rigid mold you could try the release recommended by smooth on. If there isn’t enough of a draft in your mold the part will not release easily regardless of any lubrication. The draft required will depend on the part but 3 degrees is a good starting point. If you can’t add a draft angle a soft mold (silicone as stated above) is your best bet.

Mann’s Ease Release® 200


I’ve done some draft analysis on the part, with a draft angle of 2, and because it is cylindrical there are only some very small surfaces that don’t have the correct draft angle. The cylinder has a diameter of around 20mm and is around 45mm tall, so there is a small surface around 2mm wide at the parting line of the mold where the draft angle isn’t sufficient. I’ve seen cylindrical parts injected molded before so I assumed having a small surface with not enough draft angle could be okay? Maybe I’m wrong?

I’m currently using Mann’s ease release 200 but it’s not working to well.

Thanks for the advice on the silicone mold, I’ll give that a go. I’m just hoping using a silicone mold keeps the dimensions of my part within my desired tolerances.


With the silicon mould make sure the box (you make to put the part in etc) has plenty (min 2-3cm) around it to keep its shape. You will be amazed at the replication, it’s well worth making sure your part is “perfect” before the moulding, this silicon brings over the smallest details, even fingernail scratches on the resin!

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I use STONER mold release from the alumilite corp. i also cast with a hard poluurethatne, works pretty well, but i havent testedit with any serious overhangs in the mold.

The ER200 should work but if it is still wet when you fill the mold then that might be the issue. Think you need to spray, white the mold with a soft brush and hit it again with a light spray and let dry for 5 minutes.
I have been getting my Smooth-On stuff from Reynolds, You may want to contact one of the local Reynolds and talk to a sales rep and they should be able to help right way. Usually faster than waiting for a response from Smooth-On.