Overmolding and insert

Overmolding and Insert Molding

Get custom plastic parts molded with two materials or metal inserts. Upload a part to get an online quote.

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Our overmolding and insert molding processes produce custom prototypes and on-demand production parts in as fast as 15 days. We use aluminum molds that offer cost-efficient tooling, producing parts from a range of thermoplastic and liquid silicone rubber materials.

Overmolding and insert molding are frequently used for:

Overmolding and Insert Molding Design Guidelines

Our basic guidelines for overmolding and insert molding include important design considerations to help improve part manufacturability, enhance cosmetic appearance, and reduce overall production time.

Maximum Part Size18.9 in. x 29.6 in. x 8 in.480mm x 751.8,, x 203.2mm 
Volume59 cu. in.966,837 cu. mm 
Depth4 in. form parting line101mm from parting line 
up to 8 in. if the parting line can pass through middle of partUp to 203.2mm if the parting line can pass through middle of part 
Projected Mold Area175 sq in. (plastic)112,903 sq. mm (plastic) 
48 sq. in. (silicone rubber)30,958 sq. mm (silicone rubber) 



Additional Notes

Overmolding Material Bonding

Chemical bonding between overmolded materials is possible, but material compatibility should be considered in order to achieve desired bond strength. Incorporation of an adequate mechanical bond is strongly recommended if bonding is critical to your application. An undercut is a good example of a mechanical bond.


Substrate Material
Overmold MaterialABS LustranABS/PC CYCOLOY C2950-111PC Lexan
PBT Valox
PP Profax 6323
TPU – Texin
TPV – Santoprene
TPE – Santoprene
LSR – Elastosil
3003/30 A/B
TPC – Hytrel 3078CCCCM
TPE-Versaflex OM
TPE-Versaflex OM
TPE-Versaflex OM
TPE-Versaflex OM

M = mechanical bond (recommended)
C = chemical bond

Insert Molding Capabilities

Instead of a mold that produces a final part using two separate shots like overmolding, insert molding generally consists of a preformed part—often metal—that is loaded into a mold, where it is then overmolded with plastic to create a part with improved functional or mechanical properties. We currently accept inserts from PEM, Dodge, Tri-Star, Spirol, and Tappex. A complete chart of stocked inserts at Protolabs is available here.

One way insert molding is used is with threaded inserts, which reinforce the mechanical properties of plastic parts’ ability to be fastened together, especially over repeated assembly. Bushings and sleeves are another great way to increase part durability for mating components that need more abrasion resistance due to moving parts.

What is Overmolding?

With overmolding, the production of the substrate parts is a standard injection molding process involving an aluminum mold with no heating or cooling lines running through it. Cycle times are a bit longer, which allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. When the total run of substrate parts are molded, overmold tooling is then assembled to the press. The substrate parts are placed by hand into mold where each part is overmolded with either a thermoplastic or liquid silicone rubber material.

What is Insert Molding?

Insert molding is a similar process but instead uses a preformed part—often metal—that is loaded into a mold where it is then overmolded with a thermoplastic resin to create a final component. When the run is complete, parts are boxed and shipped shortly thereafter.

Get an online quote and injection molding design analysis today.

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