The Science Behind Shrinky Dinks

Occasionally, toy creators discover simple concepts that evolve into massive hits. These toys become cultural phenomena, embedding themselves in our shared memories and appealing to multiple generations. Shrinky Dinks is a prime example of such a product.

For over four decades, Shrinky Dinks has captivated both kids and adults with its creative appeal. The process is straightforward: color a flexible plastic sheet with your design, then bake it in a warm oven to see it shrink and harden.

As you watch, the plastic film twists, curls, and distorts before gradually settling back into its original form. The key change is that your design shrinks to about one-third of its size while becoming nine times thicker. This creates a sturdy, long-lasting item perfect for countless creative projects.

Blank plastic sheets allow you to craft custom shapes and unique designs. Creative individuals use them to produce handmade Christmas ornaments, zipper pulls, jewelry, keychains, pet ID tags, and even personalized greeting cards.

Numerous manufacturers produce a wide variety of premade Shrinky Dinks designs. These include popular cartoon characters, sports team emblems, and Barbie doll figures. Themed kits are available, featuring monsters, princesses, comic book heroes, and even educational sets for teaching numbers and letters.

Regardless of the theme, every Shrinky Dinks kit contains one essential component – the so-called "magical" shrinking plastic film. This film leverages the unique properties of a specific plastic type. Without these properties, the plastic would simply burn, melt into a mess, or release harmful fumes.

Continue reading to uncover the science behind Shrinky Dinks plastics. You'll also discover how two resourceful stay-at-home moms transformed this ordinary plastic into an artistic sensation, building a multimillion-dollar global enterprise.

Decades of Shrinkage

For over 40 years, Shrinky Dinks has been a household name, with its origins tracing back to a kitchen oven in Brookfield, Wisconsin. In 1973, Cub Scout mothers Betty Morris and Katie Bloomberg were brainstorming craft ideas for their local troop.

They discovered a craft book showcasing a clever technique – drawing on plastic food container lids with permanent markers and then baking them in a warm oven. Within minutes, the plastic would curl, shrink, and flatten into a smaller, sturdier version of the original design.

The idea seemed perfect for Boy Scouts, as the women believed the children would enjoy crafting plastic Christmas tree ornaments.

Securing enough plastic for their project was difficult since the material was typically sold in large quantities to manufacturers. Morris contacted a plastics company and learned she needed to order at least 1,000 pounds. Instead, she requested a dozen sample sheets, never planning to purchase such a massive amount.

During the ornament project, something unexpected occurred. The Boy Scouts had an incredible amount of fun working with the plastic. This enthusiasm inspired Morris and Bloomberg to market the plastic as a crafts kit for kids. Each woman contributed $600 (equivalent to over $6,000 today) to purchase a bulk order of the material.

They hand-assembled $2 kits and sought out places to sell them. Initially, they considered arts-and-crafts shows, but these events required finished products, not DIY kits. After reconsidering their strategy, they took a different route, which ultimately proved successful.

From Mall to Mainstream

Despite initial rejection from craft event organizers, Morris and Bloomberg persisted. They set up a booth at a local mall, using a toaster oven to demonstrate their product, now named Shrinky Dinks. The live demos captivated shoppers, and within four months, they sold over $50,000 worth of kits under K & B Innovations. Adjusted for inflation, that’s equivalent to a quarter-million dollars today.

Their impressive sales attracted the attention of M.W. Kaasch Company, a local toy distributor, which took over manufacturing and distribution of Shrinky Dinks.

After their initial distribution deal ended, Morris and Bloomberg licensed the Shrinky Dinks brand to other companies. Major players like Milton Bradley, Golden Books, and Colorforms adopted the name for their own plastic kits. With these partnerships, Shrinky Dinks became a global phenomenon, dominating the market in the 1970s and '80s.

In 1981, Bloomberg decided to step away from the business. She leveraged her fame to enter local politics, eventually becoming the mayor of Brookfield, Wisconsin. This left Morris to manage the Shrinky Dinks empire on her own.

Licensing agreements evolved over time, prompting Morris to adopt a new business strategy. She moved away from licensing and instead focused on supplying materials. Now, any company wishing to use the Shrinky Dinks name must source the plastic directly from K & B Innovations.

Since its creation, Shrinky Dinks has been featured in 400 different products and sold in over 40 countries. In total, the company has generated approximately $150 million in sales from these plastic kits.

Now that you’re familiar with the history of Shrinky Dinks, let’s explore the science behind why this specific type of plastic behaves so uniquely and wonderfully when exposed to heat.

Polystyrene's Properties

The material used in Shrinky Dinks is known as polystyrene. It’s commonly found in cafeterias as the clear lids covering sandwiches and other foods. If you search your recycling bin, you’ll likely find plastic labeled No. 6, which is also polystyrene. By cutting, sanding, and coloring these containers, they can function just like Shrinky Dinks plastic.

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

Polystyrene has unique properties. At room temperature, it’s stiff, lightweight, and transparent, making it ideal for food containers and similar items. When heated above 375 degrees Fahrenheit (190 degrees Celsius), it melts and can be easily molded into various shapes.

Manufacturers produce plastic sheets for Shrinky Dinks using an extrusion process. This involves mixing polystyrene ingredients in a heated drum, then pushing the malleable plastic through a slot die to create sheets measuring 0.09 inches (2.3 millimeters) thick.

While still warm, the 0.09-inch (2.3-millimeter) plastic sheets are fed through rollers that compress them to 0.01 inches (0.3 millimeters) thick. The rollers are cooled, rapidly chilling the plastic and "freezing" the molecules into their stretched, flattened state.

The sheets consumers receive contain polymers eager to revert to their original 0.09-inch (2.3-millimeter) thickness. When heated, the molecules realign, shrinking the plastic to two-thirds its size while thickening. This behavior, reminiscent of memory, earns polystyrene the nickname memory plastic.

Not all plastics shrink uniformly due to production methods. Plastics stretched in one direction (axially oriented) shrink unevenly, while those stretched in two directions (biaxially oriented) return to their original shape with minimal distortion. Shrinky Dinks use biaxially oriented polystyrene to prevent designs from warping into unrecognizable forms.

Serious Shrinking

The same qualities that make polystyrene fun for children also attract scientists and researchers, though for more advanced applications. Dr. Michelle Khine, a biomedical engineer at the University of California, Irvine, has leveraged the shrinking properties of polystyrene in various projects [source: UCMerced].

Her journey began while working with microfluidics devices, which are essentially computer chips embedded with microscopic tubes acting as plumbing. Limited funding meant she couldn’t access expensive facilities to produce prototype devices quickly.

Rather than waiting for better resources, she innovated. She engraved microfluidics patterns onto polymer sheets and shrank them. As the sheets contracted, the patterns became more defined, creating intricate plumbing ideal for experiments involving cell assays or tiny fluid samples.

These devices serve critical purposes, such as affordable and rapid disease testing (especially in regions with limited medical infrastructure), assessing drug toxicity, or even cultivating stem cells.

For example, stem cells demand constant maintenance, requiring researchers to frequently replace the fluids that sustain and isolate them in small chambers. This repetitive task becomes tedious when done manually. However, with interconnected microfluidics chambers made from polystyrene, the entire process can be streamlined into a single, efficient step, accelerating research and yielding faster results.

Any scientific field relying on small, intricate components could benefit from Shrinky Dinks plastic. This is particularly true for areas like computer data storage, solar energy, or any research involving extensive trial and error. Designs can be easily applied to the plastic and then shrunk to a smaller scale suitable for testing.

The affordability of these plastic sheets allows scientists to modify designs quickly and see results in minutes rather than days or weeks.

It’s remarkable for a polymer best known as a children’s toy and packaging material. From kitchen ovens to advanced laboratories, Shrinky Dinks kits are more than just a creative pastime for kids and adults—they’re also a potential tool for addressing some of the world’s most urgent challenges.