Overmolding and Insert Molding Guide

Compare overmolding vs insert molding. Design guidelines, material compatibility, and process considerations for multi-material parts.

Overmolding vs Insert Molding

Both processes combine multiple materials in a single part but differ in method.

Overmolding

A soft material (typically TPE/TPU) is molded over a rigid substrate. The bond can be mechanical or chemical.

• Applications: Soft-grip handles, tool grips, automotive interior, gaskets
• Substrate: ABS, PC/ABS, nylon, PP
• Overmold: TPE, TPU, silicone (LSR), PP
• Bonding: Chemical for compatible pairs, mechanical uses undercuts/holes

Insert Molding

A pre-made component is placed in the mold cavity, then plastic is injected around it.

• Applications: Threaded inserts, encapsulated electronics, magnets
• Common Inserts: Brass threaded inserts, steel pins, PCB boards, magnets
• Placement: Manual (low volume), robot (high volume), strip/coil

Design Guidelines

• Substrate wall: 2-3 mm, overmold: 0.5-2 mm
• Mechanical locking via holes, undercuts, serrations
• Overmold should process at least 20C below substrate melting point
• Gate the overmold to fill from one side