You might have played with these as a kid, and I always wondered how Shrinky-Dinks worked. Why doesn’t the plastic just melt, and how does it shrink so evenly?

One of the best things about these is that you don’t have to buy the materials — you can simply recycle certain types of plastic you already have at home.

https://www.flickr.com/photos/creatinginthedark/2759781184

How do Shrinky-Dinks work?

If you grew up in the 1970s or 1980s, chances are you remember having fun with these magical little bits of plastic. You colored them in carefully, had mom fire up the oven and stick them in, and in a few minutes you had colorful miniaturized plastic shapes you could use for zipper pulls, ornaments, keychains, or just for playing around.

Shrinky Dinks were invented back in 1973 by Betty Morris of Brookfield, Wisconsin, who figured out a way to create little trinkets without making us all end up with little molten blobs of plastic on a cookie sheet. (Back in 1987, she told the story of how she created the concept.)

Better living through chemistry

Despite how awesome they look when they curl and shrink in the oven, there’s no magic involved. Shrinky Dinks are actually nothing more than sheets of polystyrene, a common type of plastic or polymer — a large molecule composed of repeating structural units.

shrinky dinks on trayThe polystyrene sheets are created through a process called extrusion — the material is heated to the melting point, then forced through a die to give it its shape. As the material is forced through the die and then cooled on rollers, the molecule chains that make up the plastic are stretched out and lined up as well — biaxially-oriented, if you want the technical term.

When you stick polystyrene in the oven, the heat causes the polymer chains to return to their most stable, random configuration — shrinking back down into a smaller but thicker piece of plastic.

While many other plastic objects simply get soft or melt entirely when heat is applied, biaxially-oriented polystyrene maintains its original mass — it just ends up thicker while taking up a smaller linear area.

Things to keep in mind

As we mentioned, not all plastics behave like this, so don’t go putting every piece of flat plastic you find in the oven. However, any clear plastic container that is marked with the “recycled plastic #6” marking is, in fact, polystyrene (styrofoam) and can be used like a Shrinky Dink (“shrink art), provided you have appropriate ventilation.

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Clamshell salad containers, meat trays, and even those the clear lids from McDonald’s pancake containers are just two examples of this material found in common places.

So buy a kit if you want, or dig through the trash and make your own brand of art!


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