How to Bake Polymer Clay: Part 4 – How Long to Bake Polymer Clay?

So you’ve made your polymer clay figures, beads, or charms and you’ve read the instructions for baking. You set your oven’s temperature and preheat the oven. You calculate how long to bake polymer clay. And you set the timer and wait. But…how can you tell if polymer clay is baked enough?

I asked my husband this question, and the cheeky sod answered back, “You know polymer clay is fully baked when the timer goes beep, beep, beep.”

Yeah, well. That’s not the answer. But seriously, how can you tell?

It’s really common for new clayers to notice how flexible their baked polymer clay is and assume that it’s not fully cured. But actually, that has nothing to do with it. All baked polymer clay is flexible to a degree after baking, and some brands are downright bendy if they’re thin enough. (It’s not so noticeable if a piece is very thick.) This is because polymer clay is actually vinyl and just like an old vinyl record, it’s flexible. (How flexible SHOULD it be? And should it always be flexible? What if you can’t bend your clay? Read more here.)

Flexible polymer clay is not underbaked
Polymer clay should be flexible when it’s fully baked. But if it breaks, it’s not baked long enough.

Polymer clay is a moldable plastigel made of PVC particles suspended in a mixture of plasticizers, fillers, stabilizers, lubricants, and colorants. It becomes less viscous (runny) as the temperature increases. That’s why body heat and summer temperatures can make polymer clay too soft. But once the temperature increases to a certain point, the vinyl particles in the clay begin to fuse together and the clay mass begins to harden. The clay must stay at the right temperature long enough for the particles to fully fuse, making a strong final result. If you don’t bake your clay long enough, the fusion will not be complete and the clay will easily break and crumble.

How Long to Bake Polymer Clay?

But how long is long enough? Underbaked polymer clay looks just like fully baked polymer clay. You can’t really tell by feel if the fusion process is complete. The only way to tell is to actually attempt to break a piece. Fully baked polymer clay will bend before it breaks.*** Underbaked polymer clay will snap in two or crumble when you try to break a piece in your hands. Now obviously that’s not the best way to check because you run the risk of breaking your clay creation. Not a good strategy!

Underbaked polymer clay will easily break, crumble, snap in two, or chip when carved or drilled.

***(Note: Sculpey Original and Sculpey III are both brittle and will often break easily with your hands, even when fully baked. I nearly always recommend using stronger clay brands such as Premo, Souffle, Fimo, Kato, CernitPardo, and PVClay when you need a strong, durable clay or if you’re having breakage issues.)

Know Your Oven

The best strategy is to know how your oven works and know how the clay behaves in it for various temperatures, times, and thicknesses of clay. First off, make sure you have a good baking setup including an adjustable oven, baking pans, and a separate oven thermometer (Affiliate Links – learn more here). Experiment with your oven to see what setting needs to be used to get the temperature that your clay requires for curing, this could be from 230°F (110°C) to 300°F (149°C). Watch the thermometer (Affiliate Link – learn more here) through the door and see what happens to the temperature throughout the baking cycle. Be aware that the temperature dial on most ovens is wildly inaccurate. Adjust your oven accordingly to get the desired temperature.

Then do some tests. Make bits of clay in various thicknesses and bake them for varying amounts of time. Keep track of it on paper (you won’t remember…trust me). And then once they’ve cooled try breaking the pieces. You’ll see right away what baking times work best for varying thicknesses of clay. You’ll also notice that the strength of clay keeps going up with bake time, too, and baking a really long time will give you much stronger clay. This is a good thing to know when you need extreme strength for a specific project.

Many people with dedicated claying ovens just adjust it to bake at one temperature and they never touch the dial after that. Others have marked where the “Fimo, Premo, and Kato” settings are on their particular oven. The bottom line, though, is to know your own particular oven.

Bake Longer “Just in Case”

Of course, if you don’t want to mess with running tests, just bake “longer”. If you ask most polymer clay pros they’ll say they bake everything for an hour. Or longer. And for thicker and larger pieces they might bake for several hours. Longer baking will NOT burn your clay. Longer baking will also lead to stronger clay projects.

If your clay is burning, the temperature of your oven is too high. Address your temperature, not your bake times!

That being said, longer bake times can cause some colors of polymer clay to darken. White and translucent can turn slightly amber or brown. Red, yellow, and fuchsia can darken. This does not mean the clay is burned. To prevent, or at least reduce this tendency, make sure you always cover your polymer clay projects while baking. This can be as simple as a piece of aluminum foil over the top or as complicated as a set of dedicated roasting pans. Covering your clay will shield it from the oven’s heat and dramatically reduce color shifts that happen during baking.

Package Recommendations

So why do the package recommendations tell you to never bake longer? Keep in mind that manufacturers have to write instructions for ALL types of consumers. And most ovens are wildly inaccurate. So they have to give instructions that give a balance between adequate curing and the very real and frustrating reality that many ovens will be too hot and could cause the clay to burn. The instructions on the package are what is going to give adequate results for most consumers. They are not designed to give the optimal results for perfect and controlled conditions. Feel free to do your best to create the best possible baking conditions for your polymer clay so that you can get the best results possible.

Fixing Underbaked Polymer Clay Projects

What if you realize that you have some underbaked polymer clay. What then? Luckily, you can bake your polymer clay again, this time at the correct time and temperature. I’ve heard that this won’t give as strong of results as if it was baked long enough the first time. But go ahead and try. It might help. Also, polymer clay can be rebaked an indefinite number of times. You can even rebake it if you’ve already added paint or sealer, in most cases.

Still Have Baking Questions?

Need baking help?

Learn about the right temperature, times ovens, and baking setups to ensure optimal results. No more broken or scorched projects!

77 thoughts on “How to Bake Polymer Clay: Part 4 – How Long to Bake Polymer Clay?”

  1. Hi Ginger, I’m having a little trouble with my clay creations. I use Sculpey brand clay and bake it according to what’s written on the packaging. However, most of my creations are of 0.4cm thickness. According to feedback given, somehow my earring posts comes off my clay earrings, taking along pieces of clay with it. I suspect it’s due to underbaking. I’m a little lost as to the temperature & time I should be baking my pieces.

    1. The temperature should be 275F/135, but you need to use a thermometer because ovens lie. The time needs to be so that the clay, itself, stays the right temperature for at least 30 minutes or so. Don’t reduce time because the clay’s thin. Also take into consideration the time the door is open, if there’s a tile that needs to warm up, how much insulation you have around the clay, etc. If you’re still struggling, this is covered in more detail in my baking tutorial here:

  2. Hi Ginger, great article, just thought I’d mention though.. if something is more viscous it’s means it’s thicker not runnier ….. to put it in simple language, viscosity is a fluid’s resistance to flow. So higher the viscosity of a liquid, the thicker it is and the greater it’s resistance to flow.

    1. Oops! Totally messed that up! (I do know the diff, so that was totally a typo.) I can’t believe nobody’s mentioned that in all these years. Thanks for letting me know. Fixed!

  3. HELP!!! Hi, I’m new to clay baking and have been playing around with simple earring designs, just general sizes and using cutters but they keep breaking and I don’t know how to fix it. I’m using a halogen oven, I bought an electric thermometer and set it so the temperature fluctuated between 135-145C, I have baked for way over an hour in some cases but they still break easily. I even went wild and tried baking at higher temperatures but again I face the same problem. They’re baked on a glass plate with a piece of parchment underneath and I put foil over the top to cover them. Please help me, it’s driving me crazy

  4. Is there a way to strengthen original Sculpey and Sculpey III? I started using these for bead projects and have so many laying around, it would be a shame to not be able to salvage them.

  5. Hi! Im brand new and just made my first pair of earrings tonite. Your baking tips are amazing! Thankyou. I am goin to bake tomorrow. Just a question where do i put the thermometer in the oven? Does it matter?
    Also i have a ceramic tile, i was goin to cover it with foil. Do i raise the foil like a dome over my earrings or it doesnt matter?
    Tia x

    1. The oven’s temp varies in different positions, so it’s best to put the thermometer as close to your item as possible. The foil needs to act as a shield, rather than a trap, so it just needs to cover the pieces. But you don’t want the foil to touch the clay or it will leave a mark.

  6. Just another thank you note. I really appreciate the time you’ve put into these experiments. I’m a scientist, and I can tell you with certainty that the plural of anecdote is not data. You definitely provide the data. By the way, my full-size oven, even on convection bake, can vary as much as 40 degrees from the set temp to actual temp. I always use a calibrated digital oven thermometer, set an over-temp alarm, and check frequently. I see that I can get as much as 20 degrees variation just from the oven cycling. I haven’t had any problems with under- or over-baking since I started doing this. Again, thanks for all the work, time, and tears you’re saving us.

  7. Nika van Tilburg

    I’ve seen some YouTube tutorials that say to partially bake 1 piece of a 2-piece charm to firm the bottom part, then add unbaked clay, shape the upper part, and bake for the full time required for the thickness of the whole charm. Is that OK, or would it be better to fully bake the first piece before adding and shaping more unbaked clay? Thank you for the information.

    1. I see absolutely no advantage to partially baking your clay at any step. The difference between fully and partially baking is mere minutes. Why run the risk of ruining your work by “saving” ten minutes? It’s just silly, to me, and it sounds like one of those things that people repeat because they think it’s what they’re supposed to say.

  8. Thanks for the information, Ginger. I was pinch hitting for a colleague a few weeks ago at a class for kids, making clay figures and key chains. The kids mage pretty elaborate figures, we popped them on the baking pan, stuck them in the oven. After a while, we took them out and when I picked them up all of the “arms” fell off or broke in two. And there was not repairing any of them. Guess what, we were using Sculptey III.
    I am going to claim that I have been vindicated! And I will go over your info with our staff.
    Thanks so much.

  9. This was great information. I am new to polymar clay and have been baking at the temperature and time on the packages, and the thin pieces brake. I watched a youtube tutorial and when the artist said she bakes for 1 hour, I was skeptical, but now I understand why.

    Thank you.

  10. Pingback: How to Make DIY Terrazzo Tile Ornaments Idle Hands Awake

  11. So much amazing information.. thanks so much!!
    I just have a question which I cant seem to find an answer for.
    I have a little bit of trouble with minor cracks… 2 or 3 may have small cracks when I get them out of the oven (out of approx 20 beads).
    But I have noticed recently that over time my beads seem to be cracking. I may go back to a round bead a few weeks later to make a necklace – and to my horror, nearly 30 beads were cracked!!!
    I do remember dropping the bag of beads on one occasion – would this cause so many breakages? Or am I doing something wrong in the baking of my beads?

    1. It could be due to the beads being too large. If they’re larger than about 1/2″, they really should have a pre-baked core. If they’re cracking after baking and becoming damaged from being dropped, then they’re not baked thoroughly enough. Check out my baking articles and make sure your oven is the correct temp and you’re baking long enough. If your beads are very large, hours of baking is not unreasonable.

      1. Hi Ginger,
        Thanks for your reply!
        My beads are 18mm diameter (.7 of an inch) but they have a hole in the centre which is approx 4mm. So they are only really 6mm thick at any one point.
        The clay says to bake them for 30 mins per 6mm (1/4inch) at 130degrees celcius (275F). So I have been basing it off their total size of 18mm and therefore baking for 1hr 30 mins.
        Does this sound reasonable? Or should I be baking longer?
        Also.. not sure how I would go about pre baking a core when the beads have a hole in them?
        Thanks so much!

        1. Yes, you’re baking the proper time. But do check your oven’s temp with a separate thermometer to be sure they’re not underbaking. You’re making pretty large beads, really, so I do think you’ll see less cracking if you prebake a core. That’s okay if the core has a hole in it. You can cover the core with your clay design and carve out the holes again. You might want to thread the beads on something (such as a skewer) while you make and bake them. Then you can remove them and clean up the hole after baking.

          All of this being said, sometimes you do have to switch clay brands. From time to time Kato and Premo are known for having batches of clay that tend to crack during baking more than other times.

          1. Oh I see. That’s interesting.. thanks for the info! I used some souffle clay the other day and it was perfect.
            Is there any way of saving these beads?? Can they be covered in some extra clay and rebaked? Or are they too weak now to do this?

          2. Oh noooo!! Ive just baked a bunch of beada and again numerous ones have cracked. Im so devastated. I cant work out what is going wrong. I have been conditioning well enough. I have a separate thermometer in the oven and it never goes over 130. Maybe I need tp try dropping the temperature?!?!

            1. The temperature is not the problem. If you continue to have small cracks that occur during baking and you are not making the beads very large (or if you’re making a pre-baked core), then the issue is the clay itself. You said that Souffle worked well. I would go with Souffle. If you continue to have problems, consider speaking with the folks at Polyform (Sculpey) and see what they suggest.

              As for repairing the cracks in your beads, you can usually give them a coating of liquid clay and rebake. The liquid fills in the tiny cracks and makes them invisible.

              If you are getting large cracks, then something else is going on and I’d love to see a photo.

              1. Hi Ginger
                Thanks for that.
                I need to work it out as it is still happening. Very frustrating indeed.
                I wpuld love to send you some photos. What would be the best way to do this?
                Thanks 🙂

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