Rotational Molding

What is Rotational Molding?

Rotational molding is a process where granular plastic material is sealed in an enclosed mold which is rotated bi-directionally in an oven. The Gravitational force keeps the plastic granules near the lowest part as all the inside surfaces of the mold rotate through that area, successively coating the heated surfaces with melting material until all of the material is evenly applied. When all of the plastic is melted the mold is cooled and then opened to remove the part. Rotomolding is inherently ideal for molding enclosed containers but is also very efficient for making other types of parts.


Corrosion & Decay Resistance – Rotomolded products are corrosion and decay resistant which lets them outperform metal and wood in many applications.

Durability – Rotomolded products are inherently flexible to withstand deformation. Colour is impregnated so scratches are not as noticeable. Maintenance is also reduced.

Greater Design Flexibility – Parts can be complex shapes which gives you more flexibility to design components that function and look the way you want. Often multiple parts can be combined into a single part which also saves cost. A wide range of part sizes can be rotational molded, from 1 gallon containers to 15,000 gallon containers.

Strength – Parts have inherently consistent wall thickness and strong, virtually stress free, outside corners.

Colour, Finish & Finishing – A wide range of colours are available. A range of surface finishes are also available, from smooth to coarsely textured. Decals can be molded into the part.

Lighter – Rotomolding materials are approximately 1/7 of the weight of steel and 1/4 the weight of aluminum.

Less Cost – Fabrication labour and surface finishing are greatly reduced. Compared to other molding alternatives, the molds for rotationally molded parts and mold modifications are significantly less costly.

Other Considerations

While rotomolded components have advantages over other component production options, the following factors need consideration when choosing to use rotomolding:
  • Rotomolded materials are subject to a 1-2% dimensional variation due to temperature and must be allowed to expand and contract.
  • Although rotomoldable materials are available with a range of strengths and components can be designed to provide structural rigidity, rotomolding materials are not as rigid as steel or aluminum.
  • Although the material has UV damage inhibitors, when used in environmental conditions with high UV exposure crazing (checking) of the surface will occur after 15-20 years of UV exposure.
  • Rotomolding is generally most cost effective for low to medium volume production (approximately 50 – 2,000 pieces per year – depending on the product) and is not cost effective for smaller volumes due the mold cost.