In sandwich injection moulding, or skin-core technology as it is also known, a fully-encased core is inserted into an outer skin component.
The skin component in the sandwich structure may consist of a material which is different from but compatible with the core, or it may consist of the same material which has been modified.

ALLROUNDER two-component injection moulding machines are used for sandwich injection moulding.

The process sequence for this is performed in two or three stages. First, the cavity is partially filled with the material that forms the outer skin. Following this, the core component is injected through the plastic core of the first material. Finally, a seal can be created in the sprue area with the first component, preventing the core material from penetrating through to the surface, and the sprue system is simultaneously cleared for the next shot.

Frequent applications are moulded parts which are in visible areas and require an outer skin with excellent appearance features and a core consisting of regranulated material, or technical parts with a hard core and a modified surface for improved handling and feel characteristics. Moulded parts with stylistic features such as a coloured core inside a transparent outer skin, can also be produced in a similar manner using the sandwich technology.