The common feature of all types of rotational moulds is that they are relatively low in cost when compared to those used for blow or injection moulding.

Rotational moulds are usually “shell type” moulds that define the outside shape and surface of the part. There are no internal cores involved.  The inside shape of the surface of the part is only determined by the varying thickness of the part wall.

As the mould must be heated and cooled during the course of each production cycle, one of the most important considerations to take into account when designing a mould is heat transfer which obviously dictates the choice of material for mould construction. The most commonly used mould shapes are:

• Sheet metal moulds.  Fabricated from steel, aluminium or stainless steel sheets.  These moulds are widely used for large and/or easy shaped products. Due to the manufacturing process, free form shapes are difficult to achieve in sheet metal moulds.
   
• CNC milled moulds. Cut from block aluminium.  This type of rotational mould is mainly used for smaller products demanding high accuracy and short lead times.  On the other hand the cost of this type of moulds is very much influenced by the size of the aluminium block, i.e. the deeper the mould-halves, the higher the cost.
   
• Cast aluminium moulds. These are the most common type mould for small to medium rotationally moulded parts.  Aluminium moulds cast from models or patterns are ideal for free form shapes, unusual shapes and special surface details that would be difficult to machine.  Cast aluminium moulds also have cost advantages when multiple moulds are required.