Multi-shot/Co-injection

Multi-shot/co-injection molding forms a single part from two or more plastics in one tool, enabling hard-soft combinations, seals, and multi-color features at scale.

Overview

Multi-shot/co-injection molding (also called multi-material, 2-shot, or co-injection molding) injects two or more plastics into a single mold to create one bonded part. The process can create hard-soft interfaces, integrated seals, color contrasts, and different material properties in specific regions without secondary assembly operations. Typical setups use rotating or index plates, multiple injection units, and precisely timed fills to control material placement and bonding.

Choose multi-shot/co-injection when you need high-volume production of parts that combine rigid structures with soft-touch grips, seals, or cosmetic accents. It reduces assembly, improves seal integrity, and locks alignment between materials, but requires more complex tooling, higher upfront cost, and careful material compatibility selection. Tooling lead times are longer, change iterations are more expensive, and design freedom is constrained by how the mold can index between shots. It fits best for mature designs, tight aesthetics, and annual volumes high enough to amortize multi-shot tooling investment.

Common Materials

  • ABS
  • Polycarbonate (PC)
  • Polypropylene (PP)
  • Nylon 6/6
  • TPE (thermoplastic elastomer)
  • TPU

Tolerances

±0.002"–±0.005" on critical dimensions, depending on part size and material pairing

Applications

  • Toothbrush handles with rigid cores and soft overgrips
  • Power tool housings with integrated rubber grips and bumpers
  • Automotive interior knobs and switches with soft-touch surfaces
  • Medical device housings with integrated seals and color coding
  • Consumer electronics bezels with multi-color branding features
  • Caps and closures with built-in soft sealing lips

When to Choose Multi-shot/Co-injection

Choose multi-shot/co-injection when you need multiple plastics permanently bonded in one part, especially rigid-plus-soft or multi-color features at medium to very high volumes. It fits when you want to eliminate secondary overmolding or assembly steps and can justify more complex, higher-cost tooling with a stable, long-life design.

vs Standard Injection Molding

Choose multi-shot/co-injection over standard injection molding when the part must integrate multiple materials or colors that cannot be achieved with simple inserts or painting. It is ideal when bond strength, seal integrity, or tactile feel between materials is critical and you want to avoid adhesive bonding or mechanical assembly.

vs Overmolding

Choose multi-shot/co-injection over traditional overmolding when you want tighter control of the interface, better repeatability, and lower cycle time at high volumes. Multi-shot keeps all operations in one tool and machine, improving alignment and reducing handling compared with molding a second operation in a separate tool.

vs Insert Molding

Choose multi-shot/co-injection instead of insert molding when all materials are thermoplastics and you want a chemical or molten bond rather than encapsulating a premade insert. It works best when you need complex material interfaces or soft-touch regions that would be difficult to achieve by placing and holding inserts in a cavity.

vs Liquid Silicone Rubber (LSR) Molding

Choose multi-shot/co-injection over dedicated LSR molding when you can meet sealing or soft-touch requirements with TPEs or TPUs bonded to thermoplastics in one mold. It is suitable when you need high-rate production of integrated seals without the temperature and tooling requirements associated with LSR processing.

vs Blow Molding

Choose multi-shot/co-injection instead of blow molding when your part is not a hollow container and requires precise features, sharp details, or multi-material interfaces. It is more appropriate for complex solid or shell parts where you want integrated soft regions, seals, or aesthetics rather than thin-walled bottles or tanks.

Design Considerations

  • Select material pairs with compatible melt temperatures and proven adhesion; confirm compatibility data with resin suppliers early
  • Define clear material boundaries and label which surfaces are Shot 1 vs Shot 2 on the drawing and 3D model to avoid quoting ambiguity
  • Maintain generous shutoff angles (3–5°) and robust steel conditions at material interfaces to reduce flash and wear between shots
  • Keep wall thickness uniform within each material and avoid sudden thickness transitions at the interface to limit sink and warpage
  • Plan gate locations and indexing/rotation strategy with the molder so both shots fill properly and cosmetic surfaces stay free of vestiges
  • Allow generous radii and avoid sharp corners at the material interface to improve bonding, flow, and tool life