The Most Common Materials For Plastic Injection Overmolding

Plastic injection molding is one of the services we offer at Firstpart to create composite plastic parts for practical uses. The overmolding process can be described as a molding process where a single part is made by molding a second material, the overmold, over a first material.

The first material, also called the substrate, could be a metal, plastic, or even rubber part. The second (overmolding) material is usually plastic, but other rubber or TPE materials can be used in the process. It is imperative to note that overmolding is not limited to two materials. At times, three materials may be used in an overmolding process to achieve aesthetic and functional targets.

Applications of Overmolding

Overmolding allows product designers to create strong and durable parts without the need for assembly. These parts are mechanically secured with the chemical bond that arises from the overmolding process. Overmolding is used for various applications that call for specific functionality and ergonomics in the product’s day-to-day use.

Materials used in Overmolding

There are many materials suitable for overmolding operations. The overmolding process uses resin pellets that must meet specific criteria to ensure product success. Some of these criteria include:

i. Bonding

The materials must be able to bond as strongly as possible. The bond must be able to withstand the application of the product.

ii. Compatibility

The chosen substrate and overmold material must be thermally, physically, and chemically compatible. This will prevent breakdowns and degradations in the part after production. 

Overmolding can be carried out in four different ways:

i. Plastic over plastic overmolding

ii. Rubber over plastic overmolding

iii. Plastic over metal overmolding

iv. Rubber over metal overmolding

The Best Materials For Overmolding

The most common choices for overmolding composite parts are:


ABS is widely used across the automotive and electronics industry for a range of overmolding operations. ABS has a low melting point that makes it ideal for injection molding and additive manufacturing solutions. It is highly recyclable, can be used with acids and alkalis, and can be finished in various ways. ABS is quickly processed, highly color compatible, and resistant to environmental and physical strains. Finally, low electrical and heat conductivity makes it widely useful for insulation purposes.


HDPE is high-density polyethylene. It is tough and durable, making it adept for a variety of applications. It is also moisture resistant and can be processed around 1830F. HDPE is particularly suited to the rigors of corrosion and physical-tasking environments. It has an excellent strength to weight ratio, high malleability, and can replace heavy materials for making large parts.


PEEK is an engineering thermoplastic that is well suited to the rigors of challenging environments. It is FDA approved, making it suitable for use in food and medicine. It has very good thermal, mechanical and chemical properties. PEEK is used in automobile gaskets, engines, pumps, compressors, and other components. 


Acrylic has decent tensile strength, excellent transparency, and affordability. It is used for optical applications in lenses, lamps, and touchscreens. Along with PEEK, acrylic is suitable for use in the food and medical industries.


PMMA is polymethyl methacrylate acrylic. It is an economical material that suits lighting and reflective applications. The material’s advantages include the excellent strength to weight ratio, high refractive index, clarity, chemical resistance, scratch resistance, and light transmissibility.

Why You Should Consider Overmolding

Overmolding comes with a wide range of advantages. Some of the reasons why you should use overmolding include:

i.  Aesthetic impacts to break up colors and patterns in design

ii.  To add flexibility to rigid parts.

iii.  To improve grip and handling ergonomics.

iv.  To cut/eliminate assembly time.

v.  To remove/eliminate the use of fasteners or adhesives.

vi.  For vibration and sound dampening

vii. Electrical insulation and safety

Firstpart Injection Molding Services

Firstpart can help you optimize your production, design, budget and supply chain to choose what is best for you. We boast of excellence, experience and diversity in plastic injection molding, insert molding and overmolding for making mass production volumes of various applications

Depending on your project, we can help you make low-cost or hardened steel tooling around budget, material and volume considerations.

Please click here to get in touch with one of our experts and receive free quotes, design and finish suggestions on your next project right away! Work with us and allow us to manage your die casting and injection molding needs and help you transition from rock solid prototypes to excellently finished die-casted products.