Overmoulding is an advanced injection moulding technique, closely related to insert moulding, but with a key difference: it involves moulding one material (usually a softer plastic or elastomer) over another pre-formed substrate or base material (often a rigid plastic or metal). It’s used to create multi-material, multi-layered parts with enhanced function, comfort, or aesthetics. For example, a soft grip handle on a hard plastic tool. 

Examples above several caps/bases with soft touch features for high end crowd management solutions, and an ampoule holder used in the medical industry.

How does the process work?

1. First, a rigid substrate (the main body or core) is injection moulded using a thermoplastic such as ABS, PC or Nylon. This part is then cooled and ejected. 

2. The base part is then placed into a second mould designed to fit the outer geometry. Placement can be manual or automatic (robotic). The second mould leaves certain areas of the substrate exposed for bonding. Careful consideration needs to be put into designing the part to allow a flow path for the second material to fill completely around the substrate.

3. A second material (often a soft TPE, TPU or rubber-like elastomer) is injected over or around specific areas of the substrate. The molten material fuses to the first layer through mechanical interlocking and sometimes chemical adhesion.

4. The part then cools and solidifies, creating a seamless bonded, dual-material component. The finished part is then ejected and may go through trimming or inspection.