Plastic resin molds and silicone resin molds — what’s the difference?

resin molds

Should I use plastic resin molds or silicone resin molds for my resin jewelry and crafts?

This is a such a good question (and an important one).  It is definitely important to know the pros and cons of each mold type before making your resin castings.

Both types of molds can work with a variety of resins, but knowing the limitations of each is essential to making sure you get the results you want.

Plastic resin molds

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

Advantages:

Inexpensive.  Plastic molds generally can be purchased for less than $10 each.  (Many for under $5!)  This is also good 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 resin crafters to start.  They are not generally complex (nooks and crannies) and are easier to care for when compared to silicone.  (wash after use and allow to dry)

Disadvantages:

Castings will not be shiny bright.  The surface of the casting that is touching the surface of the mold will NOT be shiny once it is 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 that allows this can also allow you to scratch the surface.  Something like a toothpick or a fingernail can leave a noticeable gouge if you’re not careful.

Difficult to make your own.  Unless you have a high tech system that allows you to mold the plastic, it will be almost impossible for you to make your own resin molds.

Silicone resin molds

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

Advantages:

Very flexible.  Silicone molds allow you to do very 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 are at least 2 to 3 times the price of a plastic mold.  Silicone costs much more than plastic.

Requires more care.  Silicone molds must be cleaned after use.  They should also be stored flat in a cool, dry area.

May require vacuum casting.  Unless you’re using a clear silicone mold, you might not see all the bubbles in your resin when casting it into silicone.  You might have to resort to using a vacuum casting setup to make sure all your bubbles are out before the resin starts to cure.

Like this post? You may be interested in  Advice on what resin to use

So which kind of resin mold should you choose?

If you’re a beginner, I would definitely go with a plastic mold.  They’re inexpensive and if you make a mistake (like your resin doesn’t cure), you’re not out a lot of money.

Once you get more seasoned, a silicone mold is a great ‘collection piece’ to add to your mold collection.  It will last for hundreds of castings.  Hint:  if you make a casting from your plastic mold that you really like and you want it to be shiny, complete the casting, get the shine you like, then mold it in silicone.

36 Comments

Lucille

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.

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Alice

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!

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Elayne

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?

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Katherine

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

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Tina

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.

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Annie

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”

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Annie

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

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Daphne

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…

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Katherine Swift

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

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lassiz

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 🙂

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Katherine Swift

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.

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lassiz

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

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Katherine Swift

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.

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lassiz

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

Katherine Swift

Are you sure the mold is made from silicone? What kind of resin are you using?

lassiz

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…

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Rachel

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 .

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Katherine Swift

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

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Ann

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 .

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Katherine Swift

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

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Jette håkansson

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

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Lynne Wakeley

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?

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Kay

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

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Katherine Swift

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.

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Carolyn Gastley

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.

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Lori Rotteau

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

Reply

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