Overmolding & Insert Molding

Our rapid overmolding and insert molding processes produce custom prototypes and on-demand production parts in 15 days or less. We use aluminum molds that offer cost-efficient tooling, and molded parts can be manufactured from a range of thermoplastic and liquid silicone rubber materials.

25 to 10,000+ parts
Shipped in 15 days or less
Molds start at $4,990*

*Cost includes both substrate and overmold tools. Insert molding tools start at $2,495.

Design Guidelines


• Max. part size: 8 in. by 16 in. by 8 in.*
• Max. part depth: 4 in. from any parting line**
• Max. projected mold area: 175 sq. in.
• Max. part volume: 59 cu. in.
• Min. part volume: 0.025 cu. in.
*Height may be limited if using LSR as the overmold material.
**Deeper parts are limited to a smaller outline.


• 0.5 degrees on all vertical faces
• 2 degrees works well in most situations
• 3 degrees is minimum for a shutoff
• 3 degrees is required for light texture (PM-T1)
• 5 or more degrees is required for heavy texture (PM-T2)


±0.003 in. for machining tolerance with an included resin tolerance of no less than 0.002 in./in.

If thermoplastic, then tolerances are the same as the substrate, however, if overmold is LSR, then tolerances shift to 0.025 in./in.

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 accept most common off-the-shelf inserts including PEM, Dodge, Tri-Star, Spirol and Tappex.

One way insert molding is leveraged 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.

Note: Inserts on blind holes (holes that do not go through the entire wall section) should to be designed with close-ended (blind) inserts. Open-ended inserts on blind cores have a high risk of material flashing up the inside of the inserts and impairing part function.
Insert Molding Capabilities
Insert molding capabilities

Mechanical Interlock

Chemical bonding between materials is possible with overmolding, but close attention must be paid to material compatibility in order to achieve desired bond strength. Incorporation of an adequate mechanical interlock is strongly recommended if bonding is critical to your application.
Mechanical Interlock

Wall thickness

Recommended thicknesses vary by material*:
• ABS: 0.045 in. - 0.140 in.
• Acetal: 0.030 in. - 0.120 in.
• Acrylic: 0.025 in. - 0.500 in.
• Liquid crystal polymer: 0.030 in. - 0.120 in.
• Long-fiber reinforced plastics: 0.075 in. - 1.000 in.
• Nylon: 0.030 in. - 0.115 in.
• Polycarbonate: 0.040 in. - 0.150 in.
• Polyester: 0.025 in. - 0.125 in.
• Polyethylene: 0.030 in. - 0.200 in.
• Polyphenylene sulfide: 0.020 in. - 0.180 in.
• Polypropylene: 0.025 in. - 0.150 in.
• Polystyrene: 0.035 in. - 0.150 in.
• Polyurethane: 0.080 in. - 0.750 in.
*The table is adapted from manufacturingcenter.com.

Surface finish

• PM-FO: Non-cosmetic
• PM-F1: Low-cosmetic, most toolmarks removed
• SPI-C1: 600 grit stone, 10-12 Ra
• PM-T1: SPI-C1, light bead blast
• PM-T2: SPI-C1, medium bead blast
• SPI-B1: 600 grit paper, 2-3 Ra
• SPI-A2: Grade #2 diamond buff, 1-2 Ra
PM in the table signifies a surface finish adjusted to fit the quick-turn injection molding process, where SPI (The Society of the Plastics Industry) denotes an industry-standard finish.


We use an automated CNC milling process to produce the mold for your parts, so some part corners will have a radius rather than a sharp edge. This typically does not require a change to your model, but resulting radii are identified before the mold is milled.


Our injection molding process uses ejector pins of various sizes to push the plastic part out of the mold after it has solidified. We select the sizes and arrangement of these pins to minimize the impact on your part design. Ejector pins range in size from 0.063 in. (1.6mm) to 0.5 in. (12.7mm). With overmolding, once the substrate part is ejected, it is hand loaded into a second mold.


Maximum side-core dimensions:
Width Height Pull
≤ 8.419 in. ≤ 2.377 in ≤ 2.900 in.
≤ 213.84mm ≤ 60.38mm ≤ 73.66mm


Proto Labs stocks hundreds of thermoplastic resins for injection molding that offer a variety of benefits for many different applications and industries. Note that there must be a one substrate to one overmold ratio, and the substrate and overmold can only be one material/color each.
See full list of materials.
ABS Nylon 6 Polypropylene
ABS/PC Nylon 6/12 PPA
Acetal Nylon 6/6 PPE/PS
Acetal Copolymer PBT PPS
Acetal Homopolymer PC/PBT PS
Liquid Silicone Rubber Polycarbonate

Chemical Bonding Compatibility with Overmolding

Substrate Material
Overmold Material ABS Lustran 433-904000 ABS/PC Cycoloy C2950-111 PC Lexan 940-701 PBT Valox 357-1001 PP Profax 6323 Nylon 66 Zytel 103 HSL NC010
TPU - Texin 983-000000 C C C C M M
TPV - Santoprene 101-87 M M M M C M
TPE - Santoprene 101-64

LSR - Elastosil 3003/30 A/B - - M M - M
TPC - Hytrel 3078 C C C C M M
TPE-Versaflex OM 1060X-1 C C C M M M
TPE-Versaflex OM 6240-1 M M M M M C
TPE-Versaflex OM 6258-1 M M M M M C
TPE-Versaflex OM 1040X-1 C C C M M M

M = mechanical bond recommended
C = chemical bond
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