Casting resin in a soap mold – Not a good idea!

casting resin in a soap mold

plastic soap mold

I get lots of questions about using molds, not designed for resin, including casting resin in a soap mold.  Sometimes non-traditional molds work, sometimes they don’t.  In cleaning up my studio this week, I found a plastic soap mold.  It was at that point that I thought to myself, “How a big a disaster can casting resin in this be?”

Oh, you won’t be disappointed.

mixing resin

I mixed a total of 1 1/2 ounces of Resin Obsession super clear resin in a 10-ounce plastic mixing cup.  Everything mixed well, albeit with a few bubbles.


Note:  My resin was a bit cold on the day I mixed it.  The two parts didn’t want to blend and I had to mix it more forcefully than normal.  This introduced more bubbles.  It reminded me to make sure my resin is warm before mixing to minimize bubbles in the resin.  

For this project, I decided not to add anything to this resin.  I wanted to be sure that if this didn’t work, the resin was the only factor.  I didn’t want the results to be clouded by pigments used, inclusions placed, etc.
casting resin in a soap mold
Before pouring the resin into the mold, I sprayed it with a couple of light layers of the Ultralease epoxy resin mold release.  This is my go-to mold release when I anticipate difficult demolding situations.  I used it when I cast resin into a gelatin mold and I’m convinced it was the magic bullet to help me get out those castings.

While you see 3 ounces as the capacity for this mold, I only poured in an ounce and a half of resin.  Why?  First, this mold would produce a much deeper casting than I would ever want to use as a resin embellishment.  Second, I wanted to make demolding difficult.  If it’s too easy, I won’t have learned much.

Once I finished the pour and removed the bubbles with a heat gun, I covered it with a dome and let it cure for 24 hours before demolding.

demolding resin casting from soap mold

The simple ‘twist and push from the back’ didn’t budge the cured casting.  I had to pull the mold away from the side of the resin.

Note:  If you haven’t used soap mold, the plastic is quite thin.  I would say it is very similar in thickness and flexibility to a plastic, take-out food container.

getting resin out of a mold


With molds designed for resin casting, once you have a loose edge, you can usually pull up on the edge to lift the resin out of the mold.  Doing that in this case completely destroyed the mold.


resin casting from a soap mold

And here is my finished casting.  While the resin cured fine, I was unable to demold it from the plastic soap mold.  In fact, most of the star adhered to the resin.  I was not able to get it off. I don’t think I will be casting resin in a soap mold again anytime soon.

What have you cast resin into that you were unable to demold?

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25 thoughts on “Casting resin in a soap mold – Not a good idea!

  1. Try putting the mold in the freezer, that helps sometimes in de-molding but you need to be careful if it is a really thin mold

    1. Yes, have done that myself. Wanted to show what happens under what I consider ‘normal use conditions’ of a plastic mold designed for resin casting.

  2. The worst I have tried is a candy mold. I had prepped it with release (the Easy Cast spray was all I had at the time), but then still needed to freeze it and wrestle with it to demold the pieces. The mold didn’t break but it was a major task to get the cast piece out.

    1. That’s funny, I love candy molds. Especially when they are the dark colored ones–it makes it so easy to see what you are pouring. Have had no trouble de-molding. I have found baking molds to be terrible, however. My pieces all came out cloudy even with nothing added to the resin.

  3. Thanks for taking on the many challenges that exist in the resin field. You make it easier for all of us to know what to use, how to use it & what to expect. You’ve saved all of us a lot of experimenting on our own. You are wonderfully generous and much appreciated!

  4. I wondered if something in the particular mold release you used interacted with the plastic making up this soap mold being that it looks like it almost fused to the casting in the areas where you couldn’t get it off.

    1. Great question! I don’t think that is likely. I believe it has more to do with the plastic type used for the soap mold.

  5. I use Pam on molds that I have not made myself. It does not interfere, with the resin setting. I have never had a mold that I could not get my resin out of.

    1. Hi Melinda, you have been lucky! I have found Pam is too greasy and can sometimes interfere with resin curing.

  6. Can I pour resin into a wire frame? Will it stick to the wire well? Maybe I can even weave it through. But in that case what would I set my mold on? seeing as it would be only molded by the shape of the wire instead of a real mold.

  7. I once used a very decorative clear plastic carton that was used for rolls from the grocery store. I had leftover resin so what the heck?!! Demolding did not work. Tried freezing it but it wouldn’t budge. I ended up cutting the plastic mold away from the casting as close as I could (it was all clear with a star imprint in the center and scalloped edges). It actually came out pretty cool. I use it as a coaster 🙂

  8. So I’m just 17 getting into knife making and I want to make some micarta but need a resin mold I’ve only been here for a little bit but I need to know where I can get one please.

    1. Unfortunately, I’m not aware of where you can find a knife mold. Have you thought about making your own?

  9. I had a hard, thin plastic chocolate mold that I wanted to use for resin. I had a feeling this would be the last time I used it (and I was right). Once I cast the resin, I ended up having to tear the mold to pieces.

    However, I then turned right around and used the castings to make a flexible silicone mold. Now I can make many, many more without struggling to demold.

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