Plastic vs. Silicone Resin Casting Molds: What’s the Difference?

plastic resin molds silicone resin moldsShould I use plastic resin casting molds or silicone molds for epoxy resin jewelry and crafts?

Knowing the difference between plastic and silicone molds is important to getting the results you want. Both types of molds can work with a variety of resins, but knowing the limitations of each is essential to making sure your products turn out correctly.

Here, we’ll go through an overview of both plastic and silicone resin casting molds and their pros and cons. You can use this article as a handy guide whenever you need a mold for your next project!

Plastic resin molds

These reusable resin casting molds are usually made from polypropylene or polyethylene sheet plastic. They are generally made from a template and are partially flexible.

Advantages:
  • Inexpensive. Plastic resin molds usually cost less than $10 each. (Many for under $5!) If or when you damage a mold, you’re usually not out a lot of money to replace it.
  • Easier to work with. Plastic molds are a great place for new crafters to start. They are easier to demold and care for as compared to silicone molds for epoxy resin.
Disadvantages:
  • Castings are not likely to be shiny and bright. The surface of the casting that is touching the surface of the mold may not be as shiny as you want once removed from the mold. You will either need to recoat with another layer of resin or cover with a layer of resin gloss sealer spray.
  • Can easily be scratched. While it is helpful that the plastic is flexible, the softness makes it easier to scratch the surface. Something like a toothpick or a fingernail can leave a noticeable gouge if you are not careful.
  • Difficult to make your own. Making your own plastic resin casting molds requires vacuum-forming sheet plastic around a template, which requires specialized equipment.

Silicone resin molds

These reusable molds are made from two-part silicone and can last for many years if cared for properly.

Advantages:
  • Very flexible. Silicone resin casting molds allow you to do complex castings that can be removed much more easily as compared to plastic molds.
  • Custom molds. You can purchase two-part silicone yourself and mold anything you want to (assuming you have a model).
  • Castings may come out shiny. I say “ may” here because the original model used to make the mold must be shiny. If it is (like with our geometric silicone resin molds), then your casting should come out just as shiny as the original.
Disadvantages:
  • Expensive. Silicone molds for epoxy resin and general crafting can be two to three times the price of a plastic mold.
  • Requires more care. Silicone molds must be cleaned after use and stored flat in a cool, dry area.
  • May require pressure casting. Unless you’re using a clear silicone mold for epoxy resin, you might not see all the bubbles in your resin when casting it into silicone. You might need to use a pressure casting set up to make sure all your bubbles are handled before the resin starts to cure.

So which kind of resin mold should you choose?

Either resin casting mold can get you great results. Pick the style and shape you like and start creating! Resin Obsession has lots of molds to get you started, all chosen by avid resin addicts who trust them for all their crafting.

Like this post? You may be interested in  Resin didn't cure - 12 reasons why your resin isn't curing

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Unpublished Blog Posts of Resin Obsession, LLC © 2021 Resin Obsession, LLC

61 thoughts on “Plastic vs. Silicone Resin Casting Molds: What’s the Difference?

  1. I just love all the information you share with us. This info is so valuable to both us beginners and seasoned crafters of resin.
    Thank you.

  2. Thanks, Katherine! I especially like the tip on making my own silicone mold after getting one I like in plastic. Simple, but I probably wouldn’t have figured it out on my own. Sometimes the obvious eludes me!

  3. I find the plastic molds do yield a shiny piece. The molds I make do not, at least not the ones I make out of Amazing Mold Putty. Can you suggest other kinds of mold making materials?

  4. @Elayne, the two part silicone kits may produce you a shinier casting. You can find them in our silicone section.

  5. Hi, can I use the molds as-is or do they need to be treated with something? I am asking generally about both plastic and silicone. Thanks.

  6. Could you use a food safe silicone mould for casting resin. For example a silicone ice cube mould?
    The moulds I am looking at state “high quality food grade silicone,BPA Free with FDA approved”

  7. That’s fab, thank you:) Much cheaper.
    Would I line the mould with anything? (Vaseline) and what is the best thing to clean the moulds with in between?
    Apologies for all the questions… #Newby

  8. I used DIY silicone mold that I learned from youtube. Corn starch mix silicone and dish cleaning liquid DIY silicone mold. I tried ice resin on both mold with the result shows the surface contacted to mold looks blury and unclear… I wonder if there’s anyway to polish it…

    1. Epoxy resins (which Ice is) don’t do well with polishing. Unfortunately, the blemish is most likely from the mold.

  9. Hello. I am making a clear resin casting using a custom silicon mold. The original 3D-printed objekt solid matt black,but I am trying to make clear resin “copies”. But I can’t get rid of the bubbles and the surface that in contact with the mold gets cloudy… I am a beginner from Norway so please help me 🙂

    1. Here are some reasons why you may have bubbles in your resin: 1. Be careful when mixing the resin. The best way to make sure bubbles aren’t in your final casting is to avoid creating them when mixing the resin. Carefully and deliberately stir the resin and hardener when mixing, but do not whip it. 2. The resin has reacted to something included in it. Make sure all inclusions are sealed with glue or clear tape before including in resin. 3. Remove bubbles before allowing the casting to cure. Draw them out with a toothpick or use a heat gun to get bubbles to the surface.

      1. Thanks. I i will try with å heatgun next time… 🙂 But what do you mean with inclusions..? The containers with hardner and resin?

        1. I LOVE my heat gun for getting out bubbles. I hope you will like it too. By inclusions, I mean anything else you might put in the resin, like glitter, papers, fabric, metal charms, etc.

          1. Aha… I see. No I just use resin. I am not adding enything. Maybe it reacts to the silicon I use..?

        2. Inclusions are objects you embed in your resin. They may need to be sealed with resin before you embad them.

  10. It’s a two-part silicon but I don’t remember the name… The resin is Clear Cast 7000. I saw one of your videos today so I thought I would try clear nail polish…

  11. I’m new to the Resin World. I’m very excited to try this out. My question is can I use the plastic container that my wax scents come in. There square and I’d really love to use the shape for my projects .

    1. Unlikely. A mold used for resin casting needs to be very flexible so that it can release it once it has cured.

  12. Question for silicone and uv resin with pearl pigments.
    Im having a curing problem. I made my own silicone molds with dragon skin 10. My uv resin will not cure all the way through and am not sure if its because of the silicone or the pigment.

    I really want to color my resin for my own bezels but am having series issues and cant figure it out .

    1. Unfortunately, I have no experience with UV resin in this situation and can’t offer any suggestions.

  13. Hallo , Jette from Denmark. Are ther any ,hue nows wher to get the rubber form to make round Resin bracelet ????
    Whit Regard
    Jette

  14. We,(the children and I) are making refrigerator magnets. I have a couple of silicone molds, just need to order some resin. Is the polyester one the best? or will the other one harden enough for this project?

  15. Thanks so much for the informative article! Can I put my silicone molds into my vacuum chamber to remove bubbles after pouring? Thank you!

    1. Yes, but depending on the resin you are using, it may not fully evacuate the bubbles. Depending on the resin, you may get a ‘foam’ on top instead of all the bubbles popping.

  16. Can I use a painted object to make a silicone mold without harming it? I am new to the whole process but want to make a special pendant.

  17. wondering how to get that “rising smoke” and/or “northern lights” look in resin. Is it a technique or special type of resin?

    1. I haven’t tried this, but I don’t see why not. Make sure to use a mold release and don’t use it for fondant again after casting resin in the mold.

  18. Hi Katherine,
    A totally “weird” use case I have in mind. I’d like to make some dominoes with my daughter. A bunch of them. I’d like them to be as “customizable” or decorative as my daughter wants… but at the same time be as square at the edges as possible… because she wants to also use them as “rally” dominoes… you know, stack them up to make them fall down.

    Anyways, I was wondering if resin was a practical medium for this. By that I mean:
    (1) is it possible to get “perfectly” flat/ square edges using resin with plastic or silicone molds?
    (2) How heavy would a solid resin domino be (more or less)? I mean, is it noticeably heavier than a regular domino or just heavy in general?
    (3) If on the off chance I wanted to make 1,000 dominoes, would this be a prohibitively slow medium to work with… I mean, could we make 100 a day and have enough for whatever project in like 10 days?
    (4) And the million-dollar question: Do you have molds that I could make rectangular dominoes with?

    Thanks!

      1. Thanks Katherine 🙂
        I see the depth is ¼ of an inch… I was looking up a good “standard” depth and they say .33 of an inch is best. Thanks a ton though. I will definitely stick around to learn more!

  19. Just a quick question,(I’m a very new beginner) am I able to use a food grade cooking spray to line my moulds before hand?to help with the removal?im just trying to make things as cheaply as possible.
    Thanks in advanced 😊

  20. I poured resin into a silicone agate coaster mold. It has never hardened completely! It’s not sticky, but I can bend it back and forth! I’ve never had this happen before! Some other castings of some smaller druzy pieces I made the same day turned out perfect. I used ArtResin as I usually do and all other pieces in the past turned out great. I just cannot figure it out! A floppy coaster really wasn’t what I had in mind here. LOL!

  21. I just cannot figure out what happened though. I’ve used ArtResin for over a year now and have done other coasters just like this that came out perfect! I just cannot figure out what the problem was with this one coaster! I’d really like to know what could have caused this to happen since this is a first for me. 😕

  22. It was interesting to read that silicone molds are more flexible and allow for more complex castings. I wonder if that has to do with the way that it’s mixed? It sounds silicone would be the best way to go for resin molds.

    1. That’s a great question Laurel! I’m afraid I don’t know enough about the chemistry of silicone to know if that is why that happens.

  23. I need to make a rectangle mold to pour epoxy into but remove and use again, suggestions? plastic or silicone or just a wood box with plastic lining. We are trying to make it look like brick or a miniature playhouse

  24. Hi Katherine,

    I’m trying to do a floral and fauna scavenger hunt and wanted the participants to arrange there finding in a wax cup to use as a mold. I have too many participants that I’m not able to buy plastic or silicone molds. Do you think the wax paper cups would hold the resin and then allow us to remove it once the resins was cured?
    Thank you

    1. Hi Lily, I’m not sure that will work well. I’m concerned the heat of the resin will melt your paper cup as it cures.

  25. Hi Katherine
    I am a new comer at this thank you for the info as I need to know as much as possible as I will be teaching it to students
    How long does a package take to get to Australia from you as I have to start ordering all things necessary for me to start teaching
    So you sell the plastic moulds measure cups etc I would like to start with book marks bracelets necklaces and some things that you cast in a metal holder (different shapes ) that become necklaces and you put flowers in the resin

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