Mould shrinkage is defined as the difference between the dimensions of the mould and the moulded part. It is expressed either in millimetres per millimetre or, more commonly, as a percentage.
Usually a general shrinkage value is quoted. Alternatively, two figures may be given – parallel (in line of flow) and perpendicular to the flow (cross-flow). This is particularly important in the case of glass-filled materials, for example, as there can be a significant difference between the two figures.
Other factors affecting shrinkage include part design, mould design, mould temperature, injection pressure and cycle time.