Insert Molding vs Overmolding: What is the Difference?

Insert Molding Vs Overmolding

A lot has changed ever since Hyatt invented the pioneer molding technique in the 1870s. The plastic processing industry is now characterized by complexity and effectiveness.

Virtually every manufacturing sector uses plastic products. This has led to the emergence of ingenious manufacturing, for example, insert molding and overmolding.

As molten plastic-based process, insert molding and overmolding can be confusing. In this post, we deep dive into the topic to make the differences between the injection molding processes clearer.

We look at the operating principle, material selection, and applications, among other aspects of the manufacturing solutions.

What is Insert Molding?

Insert molding is a variation of the injection molding method. It’s only uniqueness is that an insert or non-plastic part is involved. where a pre-formed component (referred to as an “insert”) is placed into the mold before the molten material is injected. The molten material then surrounds and encapsulates the insert to create a single, integrated part.

While the insert is often something as simple as threaded metal inserts, insert molding can also involve complex metal parts such as motors.

A typical insert-molding process follows this sequence:

  1. Cleaning the insert

  2. Placement of the insert into the mold cavity

  3. Supplying support to ensure that the part remains in position throughout the process

  4. Pouring the plastic resin into the molding cavity

  5. Allowing time for the inserted piece be covered by the molten plastic

  6. Removal of the inserted molded part

Applications of Insert Molding

Look around; you will see many applications of insert molding. It is evident in everyday activities that this manufacturing technique has advanced. Insert molding is widely adopted in medical, automotive, electronics, and consumer goods, among many other industries.

Medical Industry

Compared to many other materials, plastic parts are simpler to sterilize. The medical industry has realized this and extensively uses insert molding for a wide range of devices.

Apart from the sterilization solution, insert molding helps protect the delicate metal part’s surface. Medical cables and defibrillators need this kind of attention.

Some implants need to stay inside the body. Insert molding is a popular manufacturing method for these products. A good example is a pacemaker.

Advanced medicine for colonoscopy and endoscopy needs specialized equipment that is safe for human contact. Internal imaging cameras and related devices are manufactured through the insert molding method.

Here’s a list of other devices in the medical field based on insert molding:

  • Dental instruments

  • Knobs

  • Tubes

  • Prosthetics

  • Surgical implements

Automotive Industry

Insert molding is extremely popular in the automotive industry. Some of the parts that used to be made through plastic molding now have gone to insert molding. Why? The most prominent reason is the fact that this process is more cost-effective.

There are other advantages over conventional production methods including improved fuel economy (lighter components) and higher durability of the parts made through metal insert molding.


Consumer electronics

The electronic field has numerous insert molding instances. When the manufacturer wishes to protect an electronic device from the harsh environment, one solution is to place it inside a material. This design can also be called encapsulation. The electronic component is placed inside a mold, which offers vibration damping, strain relief, and so on.

Still on electronics, insert molding helps make designs less bulky and simplifies the assembly process.

Further examples of applications of this manufacturing process in this field are threaded inserts, appliance knobs, and military equipment.

Why Choose Insert Molding?

When you choose to insert mold, you get a better product in the following ways:

Insert molding is an extremely adaptable and handy manufacturing technique that offers users with many advantages.

First, the cost-efficiency of this manufacturing process is worth the consideration. The cost aspect arises because this process involves only one step. Labor costs, assembly costs, and such costs are avoided.

With rapid prototyping capability, plastic insert molding offers a chance for design changes, improvements, and incorporation of new properties, among other benefits.

The lack of the assembly process brings about another benefit – anomalies such as misalignments and product failures are almost non-existent in the metal inserts molding process. This is the main reason why insert molding is such a reliable production process.

If you are looking for product design flexibility, this technique is more reliable if you compare insert molding and overmolding. There is simply an unlimited number of setups, something that designers value a lot.

When you are looking to reduce weight and size of a product, insert molding is the method of choice. There is no need for extra components such as fasteners and connectors. Therefore, the resulting product is smaller and lighter than the conventional one.

What is Overmolding?

Overmolding is an injection molding process that fuses various plastic or rubber materials to create a finished product. In this method, the initial part is molded, allowed to cool, and then integrated with a second part while it is still in its molten state.

Overmolding is employed to provide waterproofing and insulation for a wide range of products. By eliminating the need for additional assembly, it ensures a fast and efficient production process.

Overmolded parts can be categorized into four types namely:

  • Plastic over metal

  • Plastic over plastic

  • Elastomer over plastic

  • Elastomer over metal

For the overmolding process to be successful, a few considerations are crucial. For instance, it is important to consider the surface texture and compatibility of the materials if both the top material and the substrate are plastic parts.

Mechanical bonding and chemical bonding are essential requirements. If the substrate is a metal part, the chemical and mechanical properties are not a big issue – almost any plastic material can be used.

Applications of Overmolding

PU Overmolding

From medical devices to car components, overmolding has many applications. Let us look at a few of these applications.

Medical Devices

The medical industry is characterized by the hygiene and precision of equipment. Take an example of surgical implements. These devices are built with plastic parts, which are safe. But the devices need to also be sterile to prevent infections.

These requirements have prompted the extensive use of overmolding in the industry. Popular examples of items made this way are catheters, syringes, plastic buttons on gadgets, and needles.

Hardware Equipment

Hand tools such as pliers, screwdrivers, hammers, and wrenches are made through the overmolding manufacturing process. The overmolding is typically for the handle part. Without the overmolding, it might be difficult or even impossible to use these products.

Household Goods

The applications of the overmolding process cannot be complete without a mention of household goods. We are all familiar with items such as toothbrushes, knives, food containers, and electric fans.

These are only a few examples of goods used every day at home that demonstrate the capability of this manufacturing method.

Household items with overmold material are not only convenient but also cost-effective. For instance, an overmold of plastic parts on metal for a knife is more convenient and affordable than a knife made purely from metal.


Many car parts are made through the overmolding version of injection molding. Good examples are the headrest, steering wheel, instrument panel, and gear shift knob.

Car trims bring numerous benefits, including minimizing the weight of the car. Before overmolding was extensively used in the industry, metal was the main component for these parts.

Why Choose Overmolding?

Better Aesthetics

One reason for choosing overmolding is to improve the aesthetics of a product. Because the material and color options are usually unlimited, it is possible to make a product appealing using this manufacturing process.

In other words, this method can make a product stand out from the competition. Imagine a brand logo sitting below a transparent thermoplastic elastomer (TPE) overmold.

Improved Performance

This is usually the main reason most manufacturers and users consider overmolding of different materials. Consider equipment in the hospitals, for instance, needles and surgical devices. The tactile sensitivity of these items requires the grip to be excellent.

Further, some products need to be protected from the elements for optimum performance. With a relevant cover added through overmolding, manufacturers can achieve these objectives.

Cost Effective Product

Contrary to what some may believe, the overmolding manufacturing process isn’t that expensive. Indeed, many manufacturers opt for this method because of its potential cost savings.

Knowing that they will use a sturdy overmold, manufacturers can decide to use less sturdy components inside a product. This way, they can get a highly functional and durable product with minimal manufacturing costs.

Differences Between Insert Molding vs Overmolding

While both overmolding and insert molding are techniques of incorporating different materials into a component, each has its unique features. Let us analyze where the difference lies for insert molding vs overmolding applications.

The Injection Molding Process

Overmolding is a multi-step process, also called two shot molding or double injection molding. This is because it starts with substrate molding. Once the substrate is formed and cured, a second mold is placed on top of the substrate.

As for insert molding, the second component in the process is pre-fabricated. The only action is to place it in the mold and then place a second layer around it. Insert molding is therefore a one-step process. This is the major process difference for insert molding vs overmolding.


Compared to the conventional injection molding process, both insert molding and overmolding are time-consuming. However, the insert injection mold process tends to be faster than overmolding, because it is a one-step process.

It doesn’t wait for the parts to cure before the metal inserts are introduced into the mold, meaning that its production volume is also likely to be higher. On the contrary, overmolding is a two step process. Its molded parts are prepared separately before they are combined.

Material Selection

The comparison of the two shot overmolding and insert molding also concerns the selection of the materials used. The overmolding process involves multiple materials – at least two materials. There is a substrate and at least one overmold material.

Popular overmold materials include PEEK (Polyether Ether Ketone), PP (Polypropylene), Nylon (Polyamide), and TPR (Thermoplastic Rubber).

Usually, the substrate is rigid, while the top cover is thinner and more pliable. The physical and chemical bonding of the materials is not straightforward. Some will bond effortlessly while some will have difficulties. Designers are sometimes prompted to include indents and undercuts to improve the bonding.

The insert molding process is different in that while the variety of materials is still relevant, there is a bit more freedom regarding the insert. Once you have selected a suitable insert – metal, plastic, ceramic, etc. – you can then find compatible plastic to cover the insert.

The type of insert selected depends on several factors including the material’s resistance to heat, chemical bonding, mechanical bonding, and thermal conductivity.


The production volume, production time, labor costs, and any other additional costs related to these processes can differ. Overall, the complex two shot mold tends to be more expensive because of the extra process.

If you are doing high volume production, the cost difference between insert molding and overmolding can be even more profound. The project productivity is higher and the assembly costs are lower in insert molding.


Identifying the difference between overmolding and insert molding can help you pick the most ideal design for your upcoming project. Both injection molding processes optimize the benefits that material variety brings to a product. They may also appear similar but a closer look reveals differences between insert molding and overmolding.

At ARIA MANUFACTURING LIMITED, we have the expertise for injection mold manufacturing processes. Bring your projects to us and we will handle it, whether it is in the prototype stage, production stage, or in-between.

Do you need any more information about insert molding vs overmolding? Are you interested in quality injection molded projects? Please get in touch and our team of professionals will do an excellent job for you.