What is Oyumaru?
It’s a thermoplastic from Japan that melts when you put it into hot water and then hardens as it returns to room temperature. You can make a mold from Oyumaru, or you can use Oyumaru itself in a mold to create small plastic charms. It is easy to use, requires no special tools or chemicals, and can be used over and over again.
Oyumaru feels slightly slippery and naturally has a shiny surface. The plastic is soft enough that you can dent (and cut) it with your fingernail. While flexible to an extent, it’s not bendy like silicone molds. In your hand, it feels sort of like candle wax but doesn’t make your fingers feel waxy. It reminds me of clear hot glue sticks, but a bit softer. Oyumaru is non-toxic. It is available either clear or in colors, and the packaging is typically written in Japanese. Oh, by the way, it’s pronounced “oh-you-mar-oo”. I made a special point of asking my Japanese cousin to help me with that (thanks, Miki!) Remember that there’s no accent on Japanese syllables…just say it with all the same tone…oh-you-mar-oo. You can use Google Translate app on your phone to translate the directions on the label (so cool!), or you can just guess. (Turns out that I guessed pretty closely.)
Melting and Shaping Oyumaru
Essentially, you put Oyumaru in hot water until it melts, take it out with a fork (or chopsticks for fun), then shape it in your hands. The package says to use 80°C (176°F) water, but I found that it cools down pretty rapidly and so I didn’t have any trouble just using hot water from a kettle. If it’s okay to make tea or coffee with, it is the right temperature to melt Oyumaru. But of course – be careful and don’t put it in your mouth. (As the label so helpfully tells you, in Japanese!)
Oyumaru comes in bars about ¼” (4mm) thick, and you can cut them with scissors if you need less than a full bar. Put the Oyumaru into hot water and wait a few minutes for it to soften. It will become slightly more transparent as it melts. It will not lose its shape, however. Soon it will be soft and malleable. Remove from the water and begin to shape with your hands. It will become stiffer as it cools and you might need to put it back into the hot water to get it soft enough to shape.
The water doesn’t affect the plastic. But water might damage the item that you want to mold. If so, blot the excess water. But do it quickly as the Oyumaru will get stiff quickly. Melted Oyumaru is not sticky and does not leave a residue on your hands. Now press your piece into the warm material and hold for a few minutes until the plastic cools and holds its shape. Once it’s sufficiently cool, the mold is ready to be used to make castings. If you’re in a hurry (and your item is waterproof), you can dunk it into ice water to cool it faster.
What Can You Mold With Oyumaru?
Because Oyumaru is relatively stiff, even when melted, it will not work well to create molds from soft, fuzzy, or very flexible things. So it works great to make a mold from a button, but not so well to make a mold from a leaf. (Though if you pressed a leaf into warm Oyumaru, it would take the texture of the veins quite well.) Oyumaru works nicely to make molds from small sculptures and charms, to create texture stamps, or to copy the texture of something to be impressed onto modeling clay, polymer clay, or even metal clay.
I didn’t try making two-part molds with Oyumaru, but it is possible. This video shows how to use a similar material called Blue Stuff to cast parts of a small alien figurine. This should give you some ideas of other ways you could use this material to make molds.
Using Oymaru Molds
Because Oyumaru cools quickly, you may find that it’s difficult to create large or deep molds for casting. It makes great push molds, but if you use a soft clay or dough, you might get too much distortion during unmolding. You can cast polymer clay into shallow Oyumaru molds with no mold release required, but keep in mind the distortion issue. Resin works beautifully with Oyumaru. No mold release is needed, and because Oyumaru is naturally glossy, resin comes out with a perfect shine. It makes excellent molds for casting epoxy resin. For example, you could use Oyumaru to make a mold from a bangle bracelet, then cast resin into that mold.
Oyumaru doesn’t make good flat texture sheets to be used with polymer clay and metal clay, but that’s just because it cools so quickly that it’s hard to make thin and then press onto a texture. Once it starts to stiffen, it no longer takes good impressions. But if you keep reheating the plastic in hot water as you go, you could make a thin sheet and then press a texture into it. But it might take some practice get a good result.
Where Oymaru works great with polymer clay is to create textures. You can “copy” textures from everyday objects with Oyumaru. It’s too stiff to make a flexible mat, but it works great to make a texture stamping tool. I can imagine using Oyumaru to mold a ribbon filigree shape from a picture frame. You could then push polymer clay into this mold, making multiple shapes to be used on many more picture frames.
Are Oyumaru Molds Durable?
Once you make a mold or texture with Oyumaru, you can keep it indefinitely. It doesn’t give off any residue, dry out, or melt at normal room temperatures. Once you’re done with it, though, you can just pop it back into the hot water to melt it down again and make something else. This means that Oyumaru is a perfect reusable mold material for when you want to make only a few items and don’t want to keep the mold permanently.
Because Oyumaru melts in hot water, however, you can’t bake polymer clay items in the mold. You also want to keep Oyumaru molds away from hot areas such as attics and cars in summer.
How Good Are Oyumaru Molds?
Of course, there is skill involved with making molds, so your results will likely be better with a little practice. But it’s an easy process, and you’ll get the hang of it quickly. There is no waste, so you can just melt it and re-do your mold if it’s not the way you like. But in general, Oyumaru makes molds with excellent detail. If you are making molds for resin, Oyumaru produces better castings than silicone putty molds. For polymer clay push molds, the details in the Oyumaru mold are good, and the polymer will readily take the design’s crisp lines well. But the drawback is that it can be hard to remove the clay without making it twist and distort.
Where to Buy Oyumaru
Oyumaru is an inexpensive craft item in Japan and is available in many “dollar stores.” Because individual sellers typically import small amounts, you can find it on marketplaces such as Etsy and also on Amazon. Just search for “Oyumaru.” It’s very cheap in Japan, but in the US it usually ends up costing around $8-15 for six pieces.
If you’re in the UK (and EU), Clayaround carries Oyumaru as well as Metal Clay Ltd., who also carries other thermoplastics. I just heard from Sue at Creative Journey Studios in Georgia, and they have Oyumaru in their shop. And if you’re in the EU, Happy Things has it, too. (Let me know if you know another good source.)
There are several thermoplastics on the market for DIY and crafting use. I also tested one called InstaMorph. This is a very different product with vastly different uses because the plastic itself is much harder than Oyumaru. InstaMorph comes in a resealable pouch filled with white plastic pellets. The melting process is similar; just pour into hot water and wait for the pellets to melt. The pellets turn completely clear when melted. You can then scoop them together into a ball and form the mass into a shape. Once cool, InstaMorph turns white again and is very hard. I did make a push mold with InstaMorph, but it’s not really suitable for this purpose as there is NO flex at all and you can’t un-mold anything you cast into it. But it can be used to create rigid molds.
InstaMorph does have excellent possibilities in your craft studio, however. You can use it to take textures from things and to build texture stamps for polymer clay. You can color InstaMorph with pigment pellets the company sells. It can be used to fabricate plastic pieces for broken toys, tools, etc. When the InstaMorph is in the melted state, it is a clear putty that acts like a putty or clay. You can, therefore, “sculpt” items like figurines and toys that will be hard plastic once it cools down. It could be used to make new handles for things, costume parts, and more. Your imagination is your only limit here.
There are other craft thermoplastics on the market. Some brand names are Polly Plastics, PolyDoh, PolyMorph, ThermoMorph, Friendly Plastic, and Moldamer. These may be similar to InstaMorph, or they could have different melting points and hardness after forming and cooling.
Thermoplastics with Polymer Clay?
I think both Oyumaru and InstaMorph, while very different products have great potential in the polymer clay studio. You can use both to copy textures that you want to impress into your clay projects. If you’ve used these thermoplastics with your polymer clay, I’d love to hear about it. Please tell me about it in the comments.
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Disclosure: I received the package of InstaMorph as a free sample from the company. Thanks, Brian! Also, the Amazon links in the article are affiliate links, which means I get a tiny percentage if you buy from them. As always, that doesn’t mean anyone has purchased an article or a review. My big fat opinions are all mine. 🙂