Curing experiments – Fimo results | Cara Jane Polymer Clay Curing experiments – Fimo results | Cara Jane Polymer Clay

Curing experiments – Fimo results

Posted on June 13, 2014

A long time ago I did a lot of experiments with the curing of Kato polyclay and shared the results with you in a series of blog posts.  It all started with trying to make these bangles and having issues with their durability, I am still wearing them now 3 years later so the effort was worth it.

Thin blue and white bangles

Thin blue and white bangles

I also did some testing on Fimo and the results of these experiments were published in the From Polymer to Art purple magazine. I have just realised I never shared the results with you so here they are below. I won’t share all the Kato results here – go back and check out the previous posts – but I will give  a brief summary at the end. Since I did these tests I did some further testing with Maggie Maggio who has also been dong lots of experiments with polymer properties – we’ve got plenty more tests lined up we just need more time in a day!!

Testing Fimo Soft

After testing Kato polyclay I was interested to find if changes to the curing method had similar effects on other brands. I made some specimens from well conditioned Fimo Soft polymer clay, the same dimensions as the Kato specimens; 10cm long by 6mm diameter round extruded rods. You can see a video of a test here 

I noticed even before I tested the Fimo Soft specimens that they were more flexible, less rigid than the Kato specimens.

Cure time tests

All specimens cured at 110°C (230°F)

30 minutes- breaking point weight of water – 810g, 808g
45 minutes- breaking point weight of water – 890g*

60 minutes- breaking point weight of water – 887g*

*weight of water when specimen bent out of jig.

Note that the specimens that bent out of the test jig carried less than half the weight of water of the Kato polymer clay specimens demonstrating the lower rigidity of the Fimo Soft specimens.

Cure temperature tests

All specimens cured for 30 minutes

110°C (230°F) – breaking point weight of water – 810g, 808g

130°C (266°F) – breaking point weight of water –596g*

140°C (284°F) – breaking point weight of water –787g*

*weight of water when specimen bent out of jig.

The Fimo Soft specimens were indeed much more flexible. They started to bend much sooner, bearing less weight than the Kato clay specimens. It is hard to quantify these results as they were so flexible they bent through the test jig, I would like to refine the test a little before testing more specimens. What I can say is that both increasing the cure time and increasing the cure temperature appears to make the specimens more flexible or able to carry more weight as none of these broke.


Conclusion of my experiments with Kato clay so far

Increasing the cure temperature, for a set cure time of 10 minutes, increased the strength of the specimens significantly but the specimens still all broke. Increasing the cure time meant that the specimens were much stronger and held about 2kg, or 2 litres of water before they bent so much they slipped through the test jig.  That may be to do with the increased time allowing the temperature in centre of the specimen to reach the correct temperature or some other factor, I’m not sure. I hope to do some more tests soon to investigate this, along with further tests to find the optimum cure time for different thicknesses of clay.

Summary of my experiments so far…

In many uses of polymer clay the strength of the finished product is not important; however in larger pieces or more ‘structural’ pieces (like my thin bangles) strength is important. Of course different applications will require different levels of strength and too much strength may be accompanied by a reduction in flexibility, so it is useful if you can change your cure method to suit what is required.

My experiments demonstrate how changing the curing method can enhance the strength of the finished item and I can now create bangles that are strong enough for the polishing process but have a degree of flexibility to survive life on the wrist.

There is always more to investigate; effects on polishing, effects on colour, further testing on other brands of polymer clay but hopefully the work I have presented here will help you achieve the strength you may need for your polymer clay pieces.

I’m always keen to share and discuss my investigations and findings, so come and add to the discussion in the comments


In case you are wondering why I’ve been so quiet on the blog/facebook/flickr etc this year I have been suffering with a slipped disc in my upper back. It is improving and I hope to be able to do more polymer and computer things soon! I also will have some exciting news about a 2015 UK polymer workshop event to share with you soon 🙂  Cara



  1. Holaaaaa,
    me encanta tu blog, y creo que segun los gustos que he leido en tu blog estarias interesado en la arcilla polimérica. Podras encontrar mas informacion sobre eso en mi blog.

    • sí, estoy interesado en la arcilla del polímero!

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