Throw Out the Design Rule Book — It’s Time to Embrace the Use of Undercuts

Undercuts are like the forbidden fruit of product design. They’re incredibly enticing, especially for young design students who are eager to create esoteric shapes. I specifically remember the first time I learned about undercuts back in design school. It seemed that every cool shape I wanted to create had an undercut. However, I was told that undercuts are also expensive to produce and unreliable at scale.

In fact, many designers believe in avoiding undercuts entirely due to the risk that the mold will destroy the part when it opens. Moreover, when it’s impossible to avoid them, these designers recommend workarounds like side actions or collapsible cores. In general, undercuts are seen as a problem and an irresponsible design choice.

A New Way to View Undercuts

EVA Undercuts

This perspective may be common, but that doesn’t mean it’s correct. Undercuts have widespread applications, from mechanical features like snaps and clasps to protective features like cases and sleeves. They can be internal or external features, and they can have a functional or aesthetic purpose. So though conventional wisdom tells us that the promise and potential of undercuts are not matched by practical reality, my own experience tells me the utility of undercuts is undeniableWhat needs to change is the notion that they’re always hard to manufacture.


From Obstacle to Opportunity

Plastics and other rigid materials may be inappropriate for undercuts because they can’t clear the molding. Materials like injection-molded EVA foam, by contrast, literally pop out of the molding, even if there’s a lip. The right materials transform undercuts from an obstacle into an opportunity. In the process, they open up a world of new design possibilities.

Injection-molded EVA foam adapts to both male and female undercuts, and the lines and cavity sizes are crisp and consistent. Plus, because foam can easily clear the tooling, deep undercuts of an inch or more are possible. That means it’s time to throw out the design rule book for good and embrace the amazing potential of foam undercuts.

Formerly, undercuts could elevate the cost of tooling by 15 to 30 percent. Since that cost inflated the price of the final product, designers tended to avoid undercuts in favor of cheaper (but less appealing) alternatives. It led to more affordable but less impressive products.

Now that the economy is moving ahead at full steam, price isn’t the only motivating factor for consumers. More and more, they’re looking for innovation, novelty, and quality. Moreover, they’re willing to pay more for products that look and perform the way they want. In this experience-driven economy, it makes no sense to reject a design because it contains an undercut and may cost more. That undercut may be precisely what grabs consumer attention and drives sales.

When, Where, and How to Integrate Undercuts

EVA Undercuts 02That said, every design decision requires careful consideration, and undercuts may not be appropriate for every product. It’s up to the designer to assess every detail before submitting the final design files; otherwise, delays and cost overruns could sink your project before it has a chance to swim.


Some of the variables designers need to consider include material flow, gates, and how a mold fills or sinks. They also need to account for witness lines, surface blemishes, draft, surface textures, and part warpage. Any of these elements could encourage or discourage the use of undercuts. The key is to think of undercuts as a viable design option, then submit that option to the necessary due diligence. Let the facts guide your decision instead of popular opinion.

Using the Right Material Matters

For instance, injection-molded EVA foam is an incredibly versatile material. Thanks to its durable strength, lightweight, and waterproof capabilities, it’s uniquely suitable for undercuts. The design potential is limitless, but these are a few common applications of undercut foam:

  • Cases and sleeves: Protective casing may not seem like a lucrative market — until you think of just how many people have cell phones and tablets. Because undercutting allows foam to wrap securely around another material, it provides unparalleled protection while sealing two materials together securely. Potential applications include the threads on a fastener or the clips that hold a taillight lens in place.
  • Internal cores: We all have some kind of “sports roller” in our homes that promises to reduce our back pain or enhance our yoga routine. These products rely on foam undercuts to achieve internal cores. Adjusting the size and shape of the core changes the density of the roller and its effect on the muscles. Moreover, because foam makes undercuts so adaptable, designs can be created to fit a number of consumer needs.
  • Molded one-piece accessories: Crocs are the most famous example of molded one-piece accessories, but other companies have adopted the process for different types of footwear and winter wear, too. Now, Crocs is set to introduce a softer, lighter foam that could spark a trend in foam accessories. Designers will have no trouble adapting to the demand, thanks to the wide array of undercuts that are possible with foam.

Designers are used to being told what they can’t do. Those restrictions may make business sense, but they also lead to uninspired designs. Injection-molded EVA foam bridges the gap by making sophisticated designs affordable and accessible to all. In the process, it facilitates products that couldn’t be created before. Indeed, it’s time for designers to rethink what’s possible.


Victor Lazzaro is the resident product development specialist of PopFoam, the leader in the injection molded EVA closed-cell foam process that specializes in complex geometries. As an independent designer, Victor has been consulting with PopFoam for 16 years and has worked with the company in a number of different applications.