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Structural Foam Molding vs Rotational Molding

By July 7, 2020February 28th, 2022No Comments

Structural Foam Molding vs Rotational Molding

Structural foam molding is a low-pressure injection molding process. Rotomolding uses rotation and gravity to distribute the plastic material and fill the mold.

Both processes are capable of forming large plastic pieces but that is where the similarities basically end.

Continue reading for a brief comparison of the two molding processes.

The type of parts produced.

Structural Foam Molding

Structural foam molding is used to produce small to large-sized solid parts with cellular core and solid outer surfaces.

The parts are extremely durable, impervious to the weather and resistant to impact, chemicals and corrosion.

Rotational Molding

Rotomolding is capable of producing small to large-sized hollow parts that can incorporate double walls and thicker walls at the part corners.

The finished product is strong and durable and when required the hollow parts can be filled with urethane foam to give them excellent strength, rigidity, insulation or buoyancy.


DECKED Pickup Truck Bed Storage Systems. Very robust material and process was required for this product made for the professional trades and active hard-working consumer markets.

Professional Equipment Case and Lid. Rotational molding is also often used to produce heavy-duty equipment storage and transport cases.

Common Uses

Structural Foam Molding

Large parts such as agricultural equipment and industrial panels & housings, utility cabinets, irrigation and other underground systems.

Multi-nozzle and gas-assist technology produce an attractive surface finish that is ideal for products such as consumer garden and architectural pieces or parts for commercial and recreational vehicles.

Rotational Molding

Used for a wide range of parts, from retail displays to durable components with complex geometries, such as enclosures for business, consumer and medical equipment.

The process offers versatility for product designers. Rotomolding is ideal for many products from commercial truck wheel well liners to large liquid storage tanks and more.

Structural foam molded components used on a voting machine case.

Commercial equipment enclosure produced using rotational molding.

Surface Aesthetics

Structural Foam Molding

Outer surfaces of parts may have some visible swirling in the finish. When required, gas-assisted molding can reduce and eliminate swirling.

Modern technologies and resin materials produce structural foam molded surface finishes that rival high-pressure injection molding.

Rotational Molding

Finished products have attractive outer surfaces. Molded-in graphics, colored material and surface textures are often used to improve outer cosmetics.

Cast molds allow for the use of special surface textures that can further enhance the product appearance.


Tolerance is one of the main reasons that the two different processes benefit quite different parts and products.

Structural Foam Molding

Tight tolerances of +/- 10% are achievable with high part to part consistency even on very large parts.

Rotational Molding

Close tolerances are more difficult to form and can be +/- 20% or more. Part to part consistency is not as reliable.


Structural Foam Molding

Low-pressure molding means aluminum tools can often be used to save costs but large complex molds are costly.

Tooling costs and lead times will increase when slides, undercuts, water channels or multiple nozzle entry points are required.

Rotational Molding

Cast aluminum molds are often used. This can save money and reduce tooling lead time.

CNC machined aluminum or electro formed and fabricated sheet steel tools can be used when required.

Structural foam molding tools are designed and built using a steel core needed to form the solid parts.

With rotational molding, powder or pellet plastic material is added to the mold cavity before being closed and taken through the molding process which distributes and fuses the resin to the outer surfaces of the cavity.

Cycle Times

Structural Foam Molding

Cycle times from 2 to 4 minutes even on very large-sized parts.

Rotational Molding

Cycle times of 30 to 60 minutes per part are required. Additional molds can be introduced to speed production if needed.

Multiple Part Molding

Structural Foam Molding

Large platen presses with multi-nozzle molding capabilities can mold multiple parts simultaneously. The use of a family of molds can increase design options and save costs.

Rotational Molding

Machines can hold multiple molds and run families of parts at the same time.


Structural Foam Molding

High volumes of EAU from 500 to 130,000 parts per year can be run with one tool.

Rotational Molding

Best for products with an EAU from 1,000 to 25,000. More tools can be added to increase output.

We hope these comparisons help you determine which molding process is most suitable for your product.

See more information on rotational molding here.

Or, visit our specialist website here for more details on structural foam molding.

Please give us a call if you would like to discuss the benefits of either molding technology or any of the range of custom molded plastic processes that Miles Products offers.

Call us at 801-717-5870 to discuss your program.