Insert Molding Vs. Overmolding: What is Different?

Insert molding vs. overmolding parts
Insert molding vs. overmolding parts

When using injection molding to produce parts, one of the most important decisions is having to choose between insert molding vs. overmolding. Each part production method presents pros and cons, and the best choice must be made, usually based on the type of product. In light of that, we’ve made a detailed comparison guide to help make selecting your preferred method much easier.

What is Insert Molding?

A popular product manufacturing method, insert molding refers to the process where molten material (usually plastic), is used to cover a pre-manufactured item (often metal). This can be a plastic handle over the metal part of a screwdriver, the plastic covering of an electronic connector or socket, or the plastic handle of a kitchen knife and many others.

The insert molding process will usually start with the preformed substrate called insert being positioned inside a mold. Melted plastic is then made to flow around it. Upon cooling, the plastic hardens around the insert, producing the require characteristic for the product.

Talking of the characteristics of insert molded products, here is what you could achieve when using the process; a thermally or electrically insulating handle for tools, threaded inserts that eliminate the need for taping and its associated costs, or weight reduction for metal products by incorporating plastic parts.

What is Overmolding?

Overmolding is defined as an injection molding process where, instead of making parts using a single material, manufacturers combine more than one type of plastic. As the name implies, this involves covering an already molded part with plastic, in a second process that’s conveniently called overmolding.

Unlike insert injection molding, overmolding is done in one production cycle and in this same machine. This not only helps cut costs, but also ensures stronger bond between the two dissimilar materials, especially since the substrate is normally warm and sticky.

Overmolding impacts product manufacturing in several different ways. It enables manufacturers to introduce decorative aspects such as color to a product, but more importantly, a functional aspect such as an easy-to-grip, rubber handle covering a smooth plastic surface.

Insert molding machine
Insert molding machine

Insert Molding Vs. Overmolding Difference

The difference between overmolding and insert molding includes a variation in the process steps, production speed, types of materials used and other areas such as part applications and cost. These differences, together with their effects, are explained in this overmolding vs. insert molding section.


The insert molding process uses an already manufactured part or product, which can be a tool or doctor’s implement, and made from any material that’s compatible with the process.

Overmolding is also similar, except that the part to be overmolded is not preformed but a part of the overmolding cycle. This required two sets of mold forms, one for the substrate and another for the overmold.

Due to the difference in the followed process and mold, insert molding and overmolding steps differ, both in terms of cost and other aspects. It also means one process will produce parts more quickly than the other, as you’ll learn below.

Production Speed

Comparing insert molding vs. overmolding for speed, we can see that insert molding is the faster method. Here’s why: the part to be covered with plastic is already made, and only one step is needed to complete the process.

Here were basing on the fact that the part was produced elsewhere and wasn’t a part of the process that aimed to produce the final inert molded product. Otherwise, the process would be longer. Most often, though, the part is purchased readymade.

The overmolding procedure, seeing that it’s a two part process, generally takes longer to complete. The part to be overmolded must be produced first, and that can take time. However, this can be shortened by ensuring these steps happen within the same machine or mold.

Material Types

Another difference between overmolding and insert molding is seen in the type of materials used. In insert molding, it’s almost always a metal part that’s being covered with rubber or plastic. But other materials may be used, such as wood or even plastic.

On the other hand, overmolding is basically plastic over plastic or rubber over plastic. That means the part will typically be produced using the injection molding before being overmolded as the final stage to complete its production.


Insert molded parts, owing to their different materials that include metal and plastic, are mostly used in different applications than the purely plastic parts from the overmolding method. Examples of such parts include automotive tools.

Overmolded parts are normally all plastic, as mentioned. These are used in a variety of applications that include medical to automotive or even consumer electronics and other products. The overmold material then serves to either improve the product’s look or usefulness.


With fewer steps to manufacture products, insert injection molding is a less costly process. Only a single injection step is required, and this can be done with fewer costs. Note that this also includes the cost to produce the require mold. With insert molding, tooling is simple and, therefore, less expensive.

In comparison, the overmolding process is a two-step process that, in addition to requiring more material, involves complex molds and longer production times. Overall, that translates to a more costly method to produce parts than insert molding.

But that’s considering that you’re not manufacturing the metal part used in the insert molding process. If that were needed, the costs could be different and much higher than that of overmolding, which only requires a plastic part.


Different methods are used to make plastic products today, one of them being injection molding and its types. The above comparison between insert molding vs. overmolding is aimed at indicating the things that makes the two injection molding processes different. This information should help you understand what

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