Choosing Between Gas Assist and Structural Foam Molding
Choosing the best molding process for a plastic part comes down to more than material specs or equipment availability. It’s about aligning performance goals with the right approach to molding. At DeKALB Molded Plastics, two proven methods – gas assist molding and structural foam molding – offer distinct advantages depending on your project’s design, cost, and production needs.
Understanding the differences between these two low-pressure molding techniques can clarify which direction makes the most sense. Read on to compare the processes and see how each stacks up in terms of performance, aesthetics, and manufacturability.
Structural Foam Molding: Lightweight Strength, Built to Last
Structural foam molding replaces traditional solid plastic parts with a cellular-core alternative. Using a chemical blowing agent mixed into the resin, the process forms a rigid, lightweight plastic with a solid outer shell and foamed interior. As the mixture enters the mold, it expands and presses against the cavity walls, forming a tough skin and a stable internal structure.
The end result is a molded part that weighs approximately 20% less than a comparable solid plastic component while offering three to four times the rigidity. Parts made through structural foam molding also exhibit high dimensional stability, minimal warping, and reduced internal stress, all with a cost-effective tooling approach.
Key Benefits of Structural Foam:
- Lighter weight and increased stiffness
- Lower mold cavity pressures, enabling lower-cost tooling
- Excellent strength-to-weight ratio
- Can be used with virtually any thermoplastic
- Effective for large parts or multi-cavity molds
- Produces parts suitable for painted or finished applications
Common applications include utility enclosures, panels, bases, and housings, especially where rigidity and large part size are important. The process supports wall thicknesses as low as 0.156″ and can accommodate complex geometry with consistent part integrity.
Gas Assist Molding: Hollow Channels, High Aesthetic Value
Gas assist molding also uses a low-pressure approach but operates with a different mechanism. After partially filling the mold with resin, nitrogen gas is introduced to push the material into the remaining cavity space. This technique forms hollow channels within the part, improving stiffness while reducing material use and cycle times.
Unlike structural foam, the gas remains separate from the resin. The pressure applied during the cooling phase prevents sink marks and produces sleek, high-quality surfaces. At DeKALB, we use advanced Milacron Structural Web and Bauer gas assist technologies to achieve tight control over fill rates, gas timing, and pressure distribution.
Key Benefits of Gas Assist:
- Reduced part weight with internal hollow channels
- Faster cycle times due to improved cooling
- Enhanced surface aesthetics – no sink marks or swirl patterns
- Support for complex geometries with variable wall thicknesses
- Reduced tonnage requirements, increasing equipment efficiency
Ideal applications include parts with large flat surfaces or varying wall sections (think machine covers, handles, and other intricate industrial components where cosmetic appearance and material savings are both priorities).
Comparing the Two Processes
Both methods serve similar goals: to produce large, strong plastic parts more efficiently than traditional high-pressure injection molding. But the way they achieve those results and the types of parts they excel at producing differ in some key ways.
| Feature | Structural Foam | Gas Assist |
| Core Structure | Cellular foam | Hollow gas channels |
| Surface Finish | Matte, textured | Smooth, cosmetic-grade |
| Weight Reduction | ~20% lighter | Hollow sections for weight savings |
| Rigidity | Very high | Moderate to high |
| Cycle Time | Moderate | Shorter |
| Tooling Cost | Lower | Moderate |
| Aesthetic Finish | Good | Excellent |
| Best Use Cases | Large rigid parts, painted enclosures | Handles, covers, curved or warped surfaces |
Structural foam molding leans toward strength and rigidity in larger parts, often where aesthetics are secondary to performance. Gas assist molding, in contrast, is best for parts that need dimensional complexity, visual appeal, or tighter tolerances across variable thicknesses.
Which Process Should You Choose?
If your design includes wide flat surfaces or requires consistent cosmetic appearance, gas assist may be the right fit. For projects involving very large components, parts with minimal wall variation, or aggressive cost targets, structural foam often provides the best return.
At DeKALB, we help customers evaluate both options during the early stages of development. Our engineering team works closely with yours to identify the process that will deliver the right performance, price, and quality combination.
Let’s Talk About Your Next Project
Selecting the right molding process is the first step toward long-term product success. DeKALB has the tools, experience, and flexibility to deliver structural plastic parts that meet your specific requirements, whether that’s through gas assist, structural foam, or a combination of both.
Contact us today to start the conversation.