Structural Foam: The Strength-to-Weight Advantage
Not every plastic part needs to be heavy to be strong. When performance, weight, and cost all matter, structural foam molding offers a smart, proven solution. DeKALB Molded Plastics has spent decades helping manufacturers build large plastic parts that hold up under pressure without adding unnecessary bulk.
Read on to see how the structure of the material itself makes that possible.
What Makes Structural Foam…Structural?
Structural foam isn’t a type of plastic—it’s a molding process. During production, an inert gas or chemical blowing agent is combined with molten resin. As the mix fills the mold, it expands. A solid plastic skin forms along the outer walls while the interior stays cellular, producing a rigid, lightweight structure from the inside out.
At DeKALB, we’ve refined this process 40+ years, using low-pressure injection and partial shot fills to reduce molded-in stress, support thicker wall sections, and improve dimensional consistency across even the largest parts.
Why Strength-to-Weight Ratio Matters
Engineers care about more than just strength. They need strong parts that don’t overload equipment, inflate freight costs, or require excessive material. That’s where structural foam stands out. Its internal structure gives parts high stiffness relative to their weight, an advantage in everything from industrial bins to medical device housings.
Instead of adding bulk to hit strength targets, structural foam adds structure.
Inside the Material: A Look at the Cellular Core
As the resin and gas mixture flows into the mold, it begins to expand. Where it touches the mold walls, cells collapse and form a smooth, solid outer skin. The interior stays foamed, creating a honeycomb-like core that spreads out stress and improves rigidity without the weight of a solid section.
That dual-layer structure (solid skin, cellular core) is what gives structural foam its unique balance of lightness and strength. Parts are typically 20% lighter than high-pressure injection molded parts and up to four times more rigid, with less internal stress.
Building Strength Where It Counts
Traditional injection molding fills every corner of the mold with dense plastic, whether it’s needed or not. Structural foam takes a different approach: material flows further under less pressure and supports thicker sections without sink or warp.
We regularly mold wall thicknesses between 3/16” and 3/8”, and many parts gain additional strength through integrated ribs and support structures. Instead of compensating with weight, we build in strength by design.
Structural Foam vs. Solid Plastics and Metals
Many customers come to us looking to replace parts made from metal, wood, or fiberglass. In most cases, structural foam is more efficient, not just in strength-to-weight ratio, but in process flexibility, cost, and durability.
At DeKALB, we’ve helped replace:
- Heavy metal frames with high-stiffness foam molded enclosures
- Concrete and fiberglass safety components with lighter alternatives
- Multi-part assemblies with a single, integrated molded piece
These solutions are custom engineered, produced using materials like HDPE, PP, ABS, and engineered resins, all supported by our in-house tool design and mold flow analysis.
Real-World Applications
Strength-to-weight performance is more than a theoretical benefit. Our customers rely on it in everyday use:
- Plastic guardrail blocks need to hold up on impact while remaining easy to install
- Medical housings require high rigidity and stable dimensions
- Pallets and bins must be durable, lightweight, and cost-effective for high volumes
Each application demands strength, but also benefits from reduced material use, faster cycles, and lower freight costs.
Smarter Structure. Better Performance.
Structural foam lets you do more with less: less weight, less material, and less stress on your tooling. And when engineered correctly, it delivers consistent, dependable performance across thousands of cycles.
If you’re working on a large plastic part and wondering how to hit strength goals without driving up cost, we’d love to help. Contact DeKALB to learn how structural foam molding can support your next product’s success.