A guide for product designers

If you're a product designer considering rotational moulding for the first time, there are several key design principles that will help you get the best results. Understanding these early in the design process can save time, reduce costs, and lead to a better finished product.

Wall thickness

Unlike injection moulding, rotomoulding produces parts with a natural variation in wall thickness. As a general rule, aim for a nominal wall thickness of 3-6mm. Corners and edges will tend to be thicker, while flat surfaces may be slightly thinner. Designing with this in mind will lead to better results.

Draft angles

Draft angles are important for easy de-moulding. A minimum of 1-2 degrees is recommended for external surfaces, and 2-3 degrees for internal features. More draft is always better and will improve both the manufacturing process and part quality.

Radii and corners

Sharp corners should be avoided wherever possible. Generous radii (minimum 6mm internal radius) ensure even material distribution and reduce stress concentration points. This is one of the most important design considerations for rotomoulded products.

Undercuts and complexity

Rotomoulding can accommodate some undercuts, but they add complexity and cost to the tooling. Where possible, design parts that can be de-moulded without the need for loose inserts or split moulds. That said, if your design requires undercuts, an experienced moulder can advise on the best approach.

Surface finish

The outer surface of a rotomoulded part takes on the texture of the mould. This can range from a polished finish to a textured surface. The inner surface will typically have a slightly rougher, natural finish. Consider which surfaces will be visible in your finished product when specifying surface requirements.

Talk to your moulder early

The single best piece of advice for any product designer new to rotomoulding is to involve your moulder early in the design process. At RevRoto, we offer design support and can advise on how to optimise your design for the process, potentially saving significant time and cost.

Get in touch to discuss your design with our team.