Structural foam molding

Structural foam molding

What is Strucutral Foam Injection Molding?

Structural foam molding is a specialized form of injection molding used for producing parts that have a cellular or foam core surrounded by a solid, outer skin. This method results in parts that are thicker and lighter in weight than those produced with traditional injection molding. The foamed structure provides strength and rigidity to the part, allowing for a reduction in material use without a significant sacrifice in strength.

1. Process

A plastic resin is combined with a chemical blowing agent or a gas. This blowing agent causes the formation of the foam structure during molding.

The mixture of molten plastic and blowing agent is injected into the mold.

As the material enters the mold, the heat and pressure cause the blowing agent to release gas, leading to the formation of bubbles or cells within the molten plastic. This results in the foamed core structure.

The outer layers of the material cool more quickly against the walls of the mold, forming a solid, dense skin. Meanwhile, the inner portion continues to foam and then cools, solidifying into the cellular core structure.

Once solidified, the part is ejected from the mold.

2. Advantages

The foamed core results in parts that are lighter in weight compared to solid injection molded parts.

The process often uses less plastic, leading to cost savings.

The cellular structure provides a high strength-to-weight ratio, offering increased stiffness and structural integrity.

The gradual cooling and the presence of the cellular core can reduce internal stresses and, consequently, the chances of warping and sink marks.

Structural foam molding generally requires lower injection pressures than traditional injection molding, allowing for larger parts to be molded on smaller machines.

This process is well-suited for parts that require thicker walls, which might be challenging with standard injection molding due to issues like sink marks.

3. Applications

Pallets, containers, and other large structural parts.

Interior panels, carriers, and certain structural components.

Door frames, window frames, and certain architectural elements.

Large toys, garden equipment, and certain types of furniture.

4. Considerations

Specialized venting may be needed to allow gases to escape during the foaming action.

  • Not all polymers are suitable for structural foam molding. The selected material should be compatible with the foaming process and the desired end properties.

Precise control over material temperature, injection speed, and other parameters is crucial to achieve the desired foam structure and part quality.


In summary, structural foam molding is a versatile process suitable for producing large, lightweight, and robust parts. It provides unique advantages over traditional injection molding, especially for parts with thick walls or those that require enhanced structural rigidity.

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