Must-read injection moulding: everything you need to know about insert moulding, outsert moulding and overmoulding


| 16-07-2022
Leestijd: 5 min.
There are various techniques for the injection moulding of plastic products. For example, have you heard of insert moulding and outsert moulding? In this article, we will tell you more about these manufacturing techniques: what they are used for and when to utilise each one.

Discovering our outstanding service levels

We use the initial idea assessment stage to establish so-called design specifications.

What is insert moulding?

Insert moulding involves injecting plastic in a mould onto a component made from a different material. This component is called the insert. It is often made from steel or some other type of metal. The advantage of this technique is that the insert is entirely covered by the injected plastic, and thus optimally integrated. You might think that placing the inserts inside the injection-moulding machine takes a lot of time, but that is not the case. At Rompa Group, this process is fully automated.

What is the difference with outsert moulding?

Outsert moulding is the same technique as insert moulding, with one key difference: the volume and/or surface area of the insert is greater than that of the plastic, which means only part of the insert is covered in plastic. In other words: with outsert moulding, the plastic is injected against the insert, not around it.

The injection-moulding process for insert and outsert moulding

The injection-moulding process for insert and outsert moulding is largely the same as for “standard” injection moulding. The standard process is as follows:

An injection-moulding machine injects molten plastic pellets into a mould.
The plastic solidifies with the help of a cooling system.
The press opens and the plastic components are ejected from the mould.

The difference: with insert and outsert moulding, you first place a metal component in the mould before closing it.

What materials and facilities are needed for insert and outsert moulding?

You use the same thermoplastics for insert and outsert moulding as for regular injection moulding. Generally speaking, you can also use the same mould steel, mould structure and injection-moulding machine. In some cases, however, we may opt for the use of a vertical injection-moulding machine. It uses gravity to keep the insert in place as the mould closes around it.

Get a grip on overmoulding

Besides insert and outsert moulding, there is another variant known as overmoulding. This technique is used for a wide range of applications in e.g. the medical, automotive and military sectors. Take a look at the image on the right, for instance: a gun with rubber grips on the handle. That is a typical example of overmoulding. The product always consists of two or more plastic or elastomeric materials.

The overmolding process

During the overmolding process, you start by forming the base layer (around an insert, if need be). Next, you inject the extra plastic layer (or layers) over and around the component. Depending on the compatibility of the material, you can use one or more synthetic resins to create a specific texture or a certain look.

Would you like to know more?

Are you curious to know which moulding technology is suitable for your product? Contact us today.




“Het product voldoet aan de eisen van de moderne tijd, is toepasbaar in alle marktsectoren, en is verkrijgbaar met en zonder automatisch transport van de handdoek.”

Distributiestation voor glasvezelkabels

“De verscheidenheid aan componenten die gemaakt moeten worden in combinatie met de verwerving van een grote hoeveelheid onderdelen en een meervoudig assemblageproces, zorgt voor een complexe uitdaging.”

Keeping children safe on the road

“The collaboration with Britax Römer has greatly intensified in a short period of time, partly due to the custom solutions that Rompa Group offers.”

Onze locaties

Waar vind je ons


Rompa CN

No.290, Qinglan Road
529000 Jiangmen City


Rompa CZ

Cukrovarská 494 / 39
682 01 Vyškov

Rompa CZ

Milady Horákové 2750
272 01 Kladno 1
+420(0) 312 662 041


Rompa DE

Theodor-Heuss-Straße 7
89340 Leipheim


Rompa NL

Ladonkseweg 1
5281 RN Boxtel
+31 411 661200

Rompa Design

Mijlstraat 11
5281 RN Boxtel
+31(0) 413 341 520


Rompa MX

Avenida La Noria No. 110
76220 Querétaro de Arteaga
+521 (442) 240 91 72