Can you boil polymer clay? Yes, you can. But in the immortal words of my wise guy husband, “Just because you can, doesn’t mean you should.”
Polymer clay cures when PVC particles soften in the heat, melt slightly, intertwine with plasticizer molecules, and fuse. This process starts at temperatures around 190°F (88°C), and you’ll notice the polymer clay mass becoming stiff. If you leave something at this temperature for very long, it will start to harden.
But polymer clay won’t fully fuse to form a solid, durable, flexible mass until it reaches much higher temperatures. It’s difficult to tell you exactly what temperature is required because this is a gradual process, not an either/or situation. It’s not like it’s soft at one temperature and becomes instantly hard one degree higher.
Can Boiling Polymer Clay Work?
Manufacturers recommend that you cure your polymer at least at 230°F (110 °C) for Fimo and as high as 300°F (148°C) for Kato. Experienced clayers will tell you that even these temps don’t give a strong, durable cure for short-duration baking times. Polymer clay needs both time and temperature to achieve a complete fusion of the clay mass. And generally, the hotter and longer you cure, the stronger the item will be (within reason).
As we all learned in school, water boils at 212°F (100°C). Depending on your altitude or the minerals in the water, this might vary by a few degrees. However, boiling water does not get hotter the longer it boils. It stays the same temperature. Boiling water cannot become hot enough to fully cure polymer clay. (Remember in physics…the increased energy goes into a state change and is released as steam, not by increasing the water temperature.)
Yes, I fully realize that there are people out there who recommend this. It might seem silly to those of us in the US, Canada, and much of Europe, where every home has an oven. But be aware that much of the world does not typically cook with ovens, and they are a luxury item that many homes do not have. For someone who does not have an oven, boiling seems like a great solution. And if the item will only be sitting on a shelf, it might not matter that it’s not as strong and durable as it could be. If this is you, curing by boiling may be a sufficient solution for your needs. But the finished item will be fragile!!!
A few manufacturers of smaller, regional, or niche brands of polymer clay recommend this method for curing their clay. Perhaps they have their reasons, or their products contain different ingredients.
For mainline brands of polymer clay such as Fimo, Sculpey, Kato, Cernit, DAS, CosClay, and Pardo, you will never get a full cure by boiling.
Under-cured polymer clay is fragile. It breaks easily, snapping or even crumbling when flexed. I never recommend partially curing polymer clay unless you are intentionally using this fragility in your process (such as when making crackled sheets). Polymer’s undeserved reputation for being fragile is due to undercuring, not due to polymer’s inherent properties. It’s quite strong and durable when properly cured!
Oh, and there’s one more thing to know about this. Fimo contains an ingredient that is affected by water, so it will get a white coating on the surface when you leave it in water. Never leave Fimo in water, even if it’s cured.
By the way, I once heard about making an “oven” on top of a pot of boiling water by putting a plate over the pot, placing the polymer clay item on the plate, and then putting a lid over that. I tried it. It did not work. The resulting clay was hard, but very brittle, and it snapped easily.
How to Cure Polymer Clay Instead of Boiling?
Polymer clay needs to reach the manufacturer’s recommended curing temperature for at least 30 minutes. This means the item, itself, needs to “feel” that hot for that long. Be aware that tiles, tenting, keeping the door open, cold rooms, or inaccurate ovens may make this challenging. You can learn more about this in my Baking Polymer Clay tutorial available here.
If you don’t have an oven, you can sometimes use a turkey roaster, a halogen oven, or even an air fryer. It depends on whether your appliance can reach the correct temperature and maintain it long enough to cure the polymer clay. You can learn more about that here.
The Connection you’ve been missing
Ready to level up?
Join blue bottle insiders
Join our members-only platform where hundreds of clayers “learn by doing” in an engaged and inspiring culture. We support exploration and excellence through discussion, live meetings, and a full archive.
