Shrinkies – Shrinking Recycled Plastic Artwork

How Does It Work

Polystyrene is a type of plastic, also known as #6 recycled plastic. It’s often used to make those clear boxes you see in restaurants or grocery stores for carrying food. When you heat this plastic in the oven, it starts to shrink and curl up, almost like it’s going to stick to itself, but then it flattens out again.

When we heat polystyrene, the tiny parts that make it up, called chains, go back to a jumbled-up shape. These chains have a special way of remembering this jumbled shape, even though they were stretched out and frozen in a different shape when they were first made. This is different from most things, which either get soft or melt when heated, or break down if they get really hot. Polystyrene shrinks a lot when heated, but it doesn’t lose any of its stuff (mass). It gets smaller in size, but thicker, to make up for it.

Take It Further

Shrinky Dinks® are a fun craft toy that was created in 1973 by Betty Morris from Brookfield, Wisconsin. They were super popular in the 1980s. Shrinky Dinks® are made of thin, bendy sheets of a plastic called polystyrene. Before you heat them, you can color and cut these sheets into different shapes. When you bake them in the oven, they shrink to about one-third of their original size and get nine times thicker and harder, but they still keep the colors and designs you added.

You can buy Shrinky Dinks® at stores like JoAnn™ Fabrics and Michaels©. But, you can also make something similar at home using clear plastic containers (made of recycled plastic #6) like the ones used for sandwiches and salads. You can cut, smooth, and decorate these containers just like Shrinky Dinks®. The cool thing about these toys is how the polystyrene is made into thin sheets.

The way all solid things, including plastics, turn out depends on how they are made. The temperature, the way they are made, and how fast they are made are all important. Making something out of raw materials (like turning plastic into a shape) is called processing. Most plastic sheets are made by a process called extrusion.

In extrusion, the raw material is pushed through a hot tube by a spinning screw. The material melts and is squeezed through a shape-maker, called a die, to get its final form. The raw polystyrene is heated to 190°C and pushed through a die. The film that comes out is still hot, around 100°C, so it’s soft and stretchy. To make the film stretch in two directions, it’s pulled in a way that’s different from how it came out of the machine. Then, it’s rolled up by cool rollers to make it harden quickly.