The best method of colouring rotomouldable polymers is compounding. This involves melting the polymer granules, adding a pigment Masterbatch powder, extruding the molten mixture, cooling the extrudate and pelletising.The coloured pellets are then ground to powder for moulding. Compounding provides a homogenous mix with pigment well dispersed and encapsulated. The pigment when added to the polymer in this way has little or no effect on the base properties of the polymer.Alternatively, natural powder can be ‘dry-blended’ directly with coloured pigment, usually in a high speed mixer. This can be slightly cheaper than compounded colour, but reduces the need for stock of many colours of compound. However, compared to compound colour, the individual particles of dry-blended colour produce a weaker product and one that has a colour that is less light-fast. For these reasons, Francis Ward never recommends the use of dry-blend in rotomoulding. Francis Ward commonly uses a compound blend technique which involves the addition of a percentage of compounded powder to natural powder in the mould. Mixing is achieved during moulding and the resultant parts have good colour with good mechanical properties, and the cost of coloured parts is reduced.