I've seen people making donuts and cakes from urethane foam on Japanese blogs and I too wanted to try this new medium. I've searched for it on Internet but I could find urethane foam only in USA or Japan, and they were too expensive for me. So I tried to find a substitute and I was wondering if there is any difference between urethane and polyurethane foam, which is available here in UK. Apparently there is not much difference between these two and so I bought soft polyurethane foam first. Here are photos from my first experiment:
The left ones are just foam, made with 2:1 ratio. As you can see they have lots on bubbles and they don't look right. I've tried couple of times and then I decided to change ratio to 1:1 as it said on the instruction that it is possible to make the foam harder by adding changing the ratio. I also added a bit of acrylic paint to it. As you can see on the right it was a failed experiment :) The foam was really hard but the amount of bubbles increased. The foam itself became more sticky and when I took it out of the silicone moulds I noticed that they were covered in foam leftovers. I decided to switch to plastic mould as I thought that I destroyed my precious silicone moulds (after I realized that I had to wait a bit and the foam leftovers were easily pealed off from silicone :)
You can easily see the difference between ones that were made with silicone and plastic moulds. Polyurethane shapes are smoother and bubbles are "closed" when made with plastic moulds, where foam made with silicone mould is rather "textured" and bubbles are open, just like on a sponge.
I also noticed that it was hard to control amount of bubbles that were created. Every shape was different and they looked like foamed jellies. I got a bit disappointed and did some more research. I've decided to buy urethane foam directly from Japan and then I noticed the ratio used in Japanese foam, which was 2,5 : 1. and then I thought that I've seen similar ratio 2,4 :1 which was used in medium flexible polyurethane foam, and I bought this one instead of Japanese version. Here are results:
Just foam without acrylic paint. I didn't mix enough so it didn't raise much.
Here is close up where you can see the perfect texture and bubbliness :D The foam is still flexible almost the same as the soft version. The raised bit has fallen down just a after a while, but not much. The upper top was shiny and smooth, ant the bottom one that was in contact with silicone, was matt and textured. I haven't tried this medium flexible foam with plastic moulds yet, as I'm waiting for proper donut shapes :) But I'm sure that it will produce smooth finish on both sides.
I also tried to "bake" them with sponge and acrylic paint, just like you shade normal air dry clay cookies. The top photo shows cakes made with soft urethane foam and the right one is shaded and also varnished :) Yes I think you can varnish polyurethane foam, and I even think that it is necessary to secure acrylic paint on the surface. The foam itself is water poof but the acrylic paint could be washed off and so varnishing in my opinion is the only solution. There might be other ways but I don't know them yet :D The bottom picture shows cakes made with medium soft polyurethane foam. Top ones are with mixed acrylic paint and they look the best, I think.
I'm really happy that I've finally got my perfect foam and I can't wait to start making donuts and cakes :D
I hope you enjoyed this post about my experiments and thank you for visiting my blog! :)