Molding Methods

Injection molding is one of the most common methods for producing plastic parts. Over the years, this process has been refined and adapted to suit various applications, leading to the development of several different injection molding methods. Here are some of the most common types:

Injection Molding Methods


Standard injection molding

The standard injection molding technique is a widely used method for producing parts from plastic materials. It involves melting plastic pellets and injecting them into a mold to form the desired shape.


Two shot injection molding

Two-shot injection molding, also known as double-shot or multi-shot injection molding, is a process that produces parts by injecting two different materials into a mold during the same molding cycle. This technique allows for the creation of plastic components with multiple colors, materials, or both.



Overmolding is a specialized process in injection molding where a single part is composed of multiple materials, typically two, but sometimes more. Essentially, overmolding involves molding material over a pre-existing part. This can be used for a variety of reasons, from aesthetic choices to functional improvements.


Insert molding

Insert molding is a variation of injection molding where pre-made inserts, typically made of metal but can also be of other materials, are placed into the mold before the injection of plastic. Once the molten plastic is injected, it encapsulates the insert, creating a single, integrated part.


Micro molding

Micro molding is a specialized form of injection molding that focuses on producing extremely small, intricate plastic parts. These parts are often so tiny that they can’t be seen clearly with the naked eye or can only be handled using microscopes and precision tools.


Gas assisted injection molding

Gas-assisted injection molding is an advanced form of injection molding that uses pressurized nitrogen gas to assist in the molding of plastic parts. It combines traditional injection molding techniques with the introduction of a gas (usually nitrogen) to help distribute the molten plastic resin within the mold more efficiently.


Structural foam molding

Structural foam molding is a specialized form of injection molding used for producing parts that have a cellular or foam core surrounded by a solid, outer skin. This method results in parts that are thicker and lighter in weight than those produced with traditional injection molding. The foamed structure provides strength and rigidity to the part, allowing for a reduction in material use without a significant sacrifice in strength.


Reaction injection molding

Reaction Injection Molding (RIM) is a unique molding technique used primarily for producing large, complex parts with specific performance characteristics. Unlike traditional injection molding, where pre-polymerized plastic is melted and injected into a mold, RIM involves the mixing of two or more liquid components directly in the mold where they chemically react to form a solid, final product.


Thin wall injection molding

Thin wall injection molding is a specialized molding technique used to produce plastic parts with very thin walls. “Thin wall” generally refers to walls that are less than 1mm in thickness, though this definition can vary based on the size of the part and the specific industry. This process is widely utilized in industries where lightweight, high-speed production is needed, such as packaging.


Liquid silicone rubber molding

Silicone rubber molding is a process used to produce parts from silicone rubber, which is a flexible, durable, and biocompatible material. Silicone rubber is different from organic rubbers because it is a synthetic elastomer made from a crosslinked polymer, which is reinforced with silica. This molding process is often used to produce seals, gaskets, buttons, medical devices, kitchenware, and other products that require high-temperature resistance, flexibility, and non-reactivity.


Compression injection molding

Compression molding is one of the oldest and simplest molding techniques, especially prevalent for thermosetting materials but also used for some thermoplastics. This process involves molding material (often in the form of pre-weighed pellets, granules, or sheets) by heating it and applying force.


In-mold labeling

In-Mold Labeling (IML) is a sophisticated technique used in plastic injection molding that integrates the labeling process into the molding stage, resulting in highly durable and aesthetically pleasing products.


Multi durometer molding

Multi-durometer injection molding is a specialized injection molding technique that allows for the simultaneous or sequential molding of materials with different hardness (or durometer) values into a single part. Essentially, it’s a variation of overmolding but focuses on the specific characteristic of material hardness.


Multi color injection molding

Multi-color injection molding is a process used to produce plastic parts that have multiple colors in a single component. It’s a variant of traditional injection molding that involves injecting two or more different colored materials into a single mold to produce a multi-colored part.


Rorary injection molding

Rotary injection molding is not a distinct molding method per se, but rather a variation of a standard injection molding machine with a rotating platen or table. It is commonly used in two-shot (or multi-shot) injection molding or for simultaneous injection and demolding.


Hot runner molding

Hot runner injection molding is a system used within injection molds to maintain the molten state of plastic from the injection molding machine all the way to the mold cavity, without the need of a runner. Traditional “cold runner” systems involve the plastic being injected into a primary runner, which then fills secondary runners, distributing the molten plastic to multiple part cavities. The plastic in these runners solidifies and is typically ejected with the part, leading to material waste and additional processing steps.


Cold runner molding

Cold runner molding is a method used in injection molding processes where the molten plastic travels from the injection molding machine’s nozzle into the mold cavities via a system of channels, known as runners, which are not heated. Once the molten plastic fills the cavities and cools, it solidifies, forming the desired part. At the same time, the material within the runner system also solidifies.


Push-pull injection molding

Used for producing parts with varying thickness levels, it involves two sets of molds that move in a synchronized manner to allow varying wall thickness.


Co-injection molding

Co-injection molding, sometimes referred to as sandwich molding or multi-material injection molding, is a process where two different plastic materials are introduced into a mold in sequential layers during a single molding cycle. This results in a part with a core of one material encapsulated within a skin of a different material. The process is often used to achieve specific product characteristics, such as enhanced barrier properties, reduced material costs, or improved aesthetics.


Expandable bead molding

Expandable bead molding is a molding process primarily used with expandable polymer beads, most notably expandable polystyrene (EPS) or expandable polypropylene (EPP). These materials are common for producing foam-like structures found in various applications, such as protective packaging, insulation panels, automotive components, and even helmets.


Direct injection expansion molding

Direct Injection Expansion Molding (often referred to as DIEM) is a more specific molding process related to expandable bead molding but with its distinct methodology. It’s a process that combines the benefits of thermoplastic injection molding with the weight-reducing properties of foam materials. This technique is especially popular in automotive applications, such as making lightweight foam-filled parts like door panels, bumper cores, or instrument panels.


Counter pressureinjection molding

Counter Pressure Injection Molding (CPIM), sometimes referred to as Gas Counter Pressure (GCP) molding, is a variation of the traditional injection molding process. This method is primarily utilized to achieve a higher surface quality and to reduce defects commonly associated with the standard injection molding of thick-walled parts or parts with intricate geometries.


Sequential valve gating molding

Sequential Valve Gating (SVG) molding is a specialized technique used in multi-cavity injection molding. It employs a system where each gate has an individual valve controlled by a timing system. This allows molders to control the filling sequence of each cavity independently, ensuring optimized part quality and reducing or eliminating defects, especially for large or complex parts.


Bi-injection molding

Bi-injection molding, also known as dual injection or two-material injection molding, is a process that allows for the simultaneous injection of two different materials into a single, integrated mold. This advanced technique can be used to combine different types or colors of resins into a single product, or to integrate soft and hard components into one cohesive part. The end result is a single part with multiple properties or aesthetics.

Each of these injection molding methods has its advantages and is suited for specific applications depending on the material properties required, the part design, production volumes, and the specific industry needs.

Have Questions about Plastic Injection Molding?

Please contact us, and we shall be happy to answer them!