How Shrinky Dinks Work

Shrinky Dinks reduce into a hard but slightly flexible plastic, perfect for making custom zipper pulls or charms.
Shrinky Dinks reduce into a hard but slightly flexible plastic, perfect for making custom zipper pulls or charms.
Image courtesy of Liz Vitale of

Every so often, toy makers stumble upon little ideas that turn into outlandish successes. Those toys become cultural icons, ingraining themselves into our collective consciousness and spanning generations. Shrinky Dinks is one of those products.

For more than 40 years, Shrinky Dinks has enthralled children and adults with its crafty charm. The premise is pretty basic. Color a sheet of floppy plastic to create a fun design and then slide your creation into a warm oven.

Before your eyes, the plastic film bends, warps, curls and then slowly flattens into its original shape. The difference is that your artwork shrinks by approximately two-thirds, and it's nine times thicker. The result is a more rigid and durable trinket suitable for any number of projects.

You can use blank sheets of the plastic to cut your own custom shapes and designs. Clever artists make their own Christmas tree ornaments, zipper pulls, jewelry, key chains, pet identification tags and even greeting cards.

Various manufacturers churn out many types of premade Shrinky Dinks designs, too. They feature cartoon characters, sports team logos and Barbie doll shapes. There are themed kits brimming with monsters, princesses and comic book characters, and there are even educational kits for learning numbers and letters.

No matter the theme, all of the Shrinky Dinks kits share one primary ingredient – the so-called "magical" shrinking plastic film. This film relies on the shape-shifting properties of a particular type of plastic. Without those properties, this plastic would just burn, melt into goo, or create a cloud of toxic gases in your home.

Keep reading, and you'll learn more about how Shrinky Dinks plastics work. You'll also see how two enterprising stay-at-home moms found new, artful value in this commonplace plastic, turning it into a global business that's netted millions of dollars.

Decades of Shrinkage

The project that inspired Morris and Bloomberg to invent Shrinky Dinks remains popular. People still love to bake plastic into ornaments.
The project that inspired Morris and Bloomberg to invent Shrinky Dinks remains popular. People still love to bake plastic into ornaments.
Image courtesy of Caitlin Shindler,

Shrinky Dinks has been around for more than four decades, and the legend began in the kitchen oven at a private residence in Brookfield, Wisconsin. It was 1973, and Cub Scout moms Betty Morris and Katie Bloomberg were searching for crafting ideas for their local troop.

They stumbled upon a craft book demonstrating a fun trick – use a permanent marker to draw a picture on a plastic food container lid and then pop the lid into a warm oven. After a few minutes the plastic curled, shrank and then flattened into its original shape ... only much smaller and more rigid.

It sounded like just the kind of project that would appeal to Boy Scouts. The women figured the kids would get a kick out of making plastic Christmas tree ornaments.

Getting enough of the plastic for their project, though, proved to be a challenge because the material was generally sold in bulk to manufacturers. Morris called a plastics company, which told her that she'd need to place a minimum order of 1,000 pounds. She requested a dozen sample sheets instead, never intending to actually buy half ton of the stuff.

But a funny thing happened during their ornament project. The Boy Scouts had a crazy amount of fun playing with the plastic. So much fun, in fact, that Morris and Bloomberg decided to try and sell the plastics as a crafts kit targeted at children. Each woman rounded up $600 (a total of more than $6,000 after accounting for inflation) and they bought an order of the plastic.

Then they assembled the $2 kits by hand and began looking for places to sell their wares. They originally considered arts-and-crafts shows, but the organizers of those events required finished products, not kits for making art. After some thought, they tried a different approach, and, as you'll see, it paid off.

From Mall to Mainstream

Some Shrinky Dinks kits come with designs already printed on the plastic. All you have to do is color them in and pop them in the oven.
Some Shrinky Dinks kits come with designs already printed on the plastic. All you have to do is color them in and pop them in the oven.
Image courtesy Brayden Mooney

Although craft event organizers weren't keen on Shrinky Dinks kits, Morris and Bloomberg didn't give up. Instead, they set up a booth at a local shopping center. To hook passersby, they brought along a toaster oven and conducted live demonstrations of their product, which was now officially called Shrinky Dinks. People were immediately intrigued, and within four months, Morris and Bloomberg had sold more than $50,000 worth of their kits under the name K & B Innovations. In today's cash value, those ladies had already hauled in a cool quarter of a million dollars.

With those kinds of sales, it was no surprise that they caught the attention of a local toy distributor, M.W. Kaasch Company, which agreed to manufacture and distribute Shrinky Dinks.

Years later, when the first distribution deal ended, the two began licensing their brand name to other companies, which applied the Shrinky Dinks name to their own plastics kits. Major companies, including Milton Bradley, Golden Books and Colorforms, bought into the Shrinky Dinks craze. With major manufacturers backing the product, Shrinky Dinks hit the big time. The 1970s and '80s saw the kits all over the country and all over the world.

In 1981, Bloomberg decided that she'd had enough dinking around. She quit the business and put her notoriety to use, running for local office and eventually becoming the mayor of Brookfield, Wisconsin. That left Morris in charge of the Shrinky Dinks empire.

Licensing agreements came and went, and Morris decided to try a different business model. Instead of focusing on licensing, she shifted to supplying materials. Now, all companies that want to use the Shrinky Dinks name are required to purchase the plastic directly from K & B Innovations.

Since its inception, Shrinky Dinks has appeared in 400 different products and been sold in more than 40 countries. In all, the company has sold about $150 million worth of those plastics kits.

Now that you know the story behind the Shrinky Dinks enterprise, it's time to pick apart the science of why this one type of plastic has such strange and wonderful properties in the presence of heat.

Polystyrene's Properties

Despite all the warping and shifting that the plastic does as it shrinks, when it flattens out, the details of the original art remain.
Despite all the warping and shifting that the plastic does as it shrinks, when it flattens out, the details of the original art remain.
Image courtesy Ben Badgett

The plastic that's used in Shrinky Dinks is called polystyrene. You'll see it frequently in cafeterias – it's used for the clear lids that protect sandwiches and other foods. If you dig through your recycling bin, you'll almost certainly come up with recycled plastic No. 6. That's polystyrene, too. In fact, by simply cutting apart these containers, sanding and coloring them, they'll work just like the plastics in Shrinky Dinks.

All plastics are polymers, which are long chains of repeating molecules. Polystyrene, like so many plastics, is made from petroleum-based chemistry.

Polystyrene has some distinct characteristics. At room temperature, it's rigid, lightweight and transparent, making it well-suited for food containers and similar products. When warmed to temperatures above 375 degrees Fahrenheit (190 degrees Celsius), polystyrene melts and can easily be manipulated into many shapes.

To make sheets of plastics like those needed for Shrinky Dinks, manufacturers use an extrusion process. In short, that means they load all of the ingredients for polystyrene into a heated mixing drum, which then forces the pliable, rubbery plastic through a slot die, creating sheets that are 0.09 inches (2.3 millimeters) thick.

While the sheets of 0.09-inch (2.3-millimeter) plastic are still warm, the machine feeds them through a roller that compresses the sheets down to 0.01 inches (0.3 millimeters) in thickness. And here's where the true magic of the process happens. Those rollers are cooled, meaning they quickly chill the freshly compressed plastic, in essence "freezing" the plastic molecules into their stretched and flattened form.

What consumers receive, then, are sheets of polymers just begging to return to their original extruded 0.09-inch (2.3-millimeter) shape. When heated in ovens, that's exactly what happens. Warmed to a more flexible condition, the molecules realign themselves and return to a thicker sheet that's two-thirds smaller. It's as if the polystyrene remembers its original form. That's why some people refer to polystyrene as memory plastic.

Not all plastics shrink evenly, and that's partly because of production conditions. In stretching the plastics, manufacturers can pull them in just one direction (called axially oriented) or two directions (biaxially oriented). When warmed, polymers that are axially oriented shrink unevenly. Those that are biaxially oriented, however, return to their original shape without much distortion. Shrinky Dinks require biaxially oriented polystyrene – otherwise, when shrunk, your cute cartoon characters might take on nightmarish proportions.

Serious Shrinking

Another example of science and Shrinky Dinks coming together: These earrings represent the chemical compound thujone.
Another example of science and Shrinky Dinks coming together: These earrings represent the chemical compound thujone.
Image courtesy Stephanie Phillips; earrings by Gina Rickicki

The same properties that entice kids to play with polystyrene also appeal to scientists and researchers, but for much more serious purposes. Dr. Michelle Khine, who works at the University of California, Irving, is a biomedical engineer who has utilized the shrinking effects of polystyrene in several projects [source: UCMerced].

It all started when she was working with microfluidics devices, which are basically computer chips interlaced with tiny tubes that serve as plumbing. With limited funding, she lacked the type of pricey facilities capable of quickly cranking out prototype devices to keep projects moving forward.

Instead of waiting for better circumstances, she improvised. She etched microfluidics patterns onto the polymer sheets and then shrank them. As the sheets shrank, the patterns on them bulged and became more pronounced. Those etchings in effect become the minute plumbing perfect for experiments requiring cell assay or very small samples of body fluids.

Ultimately, these kinds of devices are used for important purposes. They can be designed to test for diseases inexpensively and quickly (particularly in countries where medical facilities are substandard), determine drug toxicity or even help culture stem cells.

Stem cells, for instance, require a lot of constant upkeep, as researchers must continually change the fluids that nourish and suspend the cells in tiny, separated chambers. When that process has to be done for each individual group of cells, it's time-consuming drudgery. With sophisticated, interconnected microfluidics chambers created on polystyrene, the process can be completed in one quick, clever step. That speeds up research, which in turns speeds up results.

Really, any sort of science that relies on small, intricate components might benefit from Shrinky Dinks plastic. That's especially true for anyone who works with computer data storage, solar energy or other research that necessitates a lot of trial and error. Designs are easily applied to the plastic and then they are shrunk to a much smaller size that suits testing.

Best of all, the sheets of plastic are so inexpensive that scientists can change their designs on the fly and see their work in action in just minutes instead of days or weeks.

It's heady stuff for a polymer that's most popularly known as a children's toy and packaging material. From home ovens to high-tech labs, Shrinky Dinks kits aren't just a fun diversion for artsy kids (and adults). They're potentially a tool to solve some of the world's pressing problems, too.

Author's Note: How Shrinky Dinks Work

Play time and serious research have often intersected. Sometimes it's the fun that accidentally leads to scientific breakthroughs. Other times, as with Shrinky Dinks, an established industry product finds an entirely new market thanks to playful, fresh eyes. Furthermore, Shrinky Dinks are proof that plastics like polystyrene are an indispensable aspect of our current society.

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