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Plastic Extrusion Process and Design Crash Course

Learn about the plastic extrusion manufacturing process, how it works, and get tips for optimizing your plastic extrusion designs.

Joel Schadegg - Xometry Contributor
By Joel Schadegg
January 13, 2023
 6 min read
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What is Plastic Extrusion?

Plastic extrusion is a manufacturing method used to make products by forcing material through a die that forms a continuous profile matching the die as it is extruded. The process shares similarities to metal extrusion; however, instead of producing a metal product, it is designed for creating products made from plastic polymers. There are plastic extruded parts all around us in our everyday lives; for example:

  • Plastic tubes and piping (e.g., PVC plumbing)
  • Deck railing
  • Plastic gutters
  • Plastic films and sheets
  • Wire insulation

How Does Plastic Extrusion Work?

Plastic extrusion involves several stages, from melting and extrusion to cooling and processing stages. It begins with loading raw material, typically polymer resin pellets, into a hopper. Additives such as fillers and coloring agents are mixed in with the resin pellets to create a homogenous mixture for melting and extrusion. Similar to plastic injection molding, a hopper of plastic pellet material feeds a barrel containing a rotating screw that works to push the material forward. As the material passes between the screw and the barrel walls, it undergoes shearing forces and friction, which heats and begins melting. Heaters on the barrel apply additional heat, assisting the melting process. Drag forces generated by the screw force the melted polymer through a filter and breaker plate to remove contaminants and create an even distribution of polymer through the die assembly at the barrel’s end.

Slide 1 of 1
Illustration of the plastic extrusion process melting and extrusion stage.
Illustration of the plastic extrusion process melting and extrusion stage.
Illustration of the plastic extrusion process melting and extrusion stage.

Illustration of the plastic extrusion process melting and extrusion stage.

Melted plastic is shaped and formed into the profile of the exit die opening. At this stage, the extrusion is still hot and malleable. The material passes through a cooling bath filled with water which uniformly cools and solidifies the extrusion, helping bring it to its final shape. Air or metal contact cooling systems are also sometimes used. A vacuum sizing stage before the cooling stage may be necessary for extrusions that contain hollow features to mitigate defects and maintain shape. Pull rollers apply a uniform pulling pressure which helps smooth the plastic and move it further down the line. The plastic extrusion receives quality control checks using onboard laser measurement systems, and good sections are then spooled or cut to final part dimensions. The product is then ready for final quality checks, storage, and packaging.

Plastic Extrusion Design Tips

A well-thought-out design can reduce costs, mitigate defects, and ultimately lead to a higher-quality product. In the sections below, we will go over tips and considerations when designing a part for the plastic extrusion process.

Slide 1 of 1
Extrusion design with uneven wall thickness vs. uniform wall thickness.
Extrusion design with uneven wall thickness vs. uniform wall thickness.
Extrusion design with uneven wall thickness vs. uniform wall thickness.

Extrusion design with uneven wall thickness vs. uniform wall thickness.

Wall Thickness

Pro Tip: Design with uniform wall thicknesses. Wall thickness should not be less than 0.025"-0.050", depending on part size.

With extrusion processes, it is crucial to maintain relatively even cooling rates across the profile as it is extruded. If cooling is uneven in areas, it can lead to defects such as warping and twisting and cause features to fall out of specification. One of the best ways to create a balanced extrusion with even cooling is to design using uniform wall thicknesses. Uneven walls can affect the flow of the material and cause uneven cooling, so the more uniform the walls are, the better.

Another factor to keep in mind with wall thickness is the minimum wall thickness. Extremely thin-walled parts can be very challenging or impossible to produce efficiently, leading to issues. Minimum wall thickness scales with overall part size, so the larger the part, the thicker the walls need to be to support the profile. For smaller parts, a wall thickness between 0.025"-0.030" is typically suitable, while for larger parts, you will want to increase the minimum thickness to around 0.040"-0.050".

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Diagram of an extrusion cross-section depicting proper use of corner radii
Diagram of an extrusion cross-section depicting proper use of corner radii
Diagram of an extrusion cross-section depicting proper use of corner radii

Diagram of an extrusion cross-section depicting proper use of corner radii

Corner Radii

Pro Tip: Never leave corners completely sharp; use a radius of 0.016” or larger.


Radii help promote good material flow as it is extruded through the exit die. If corners are left completely or excessively sharp, it can create a concentrated area of stress. These stress concentrations lead to issues such as breaking and warping in the extrudate. That said, designers should always add radii to sharp corners to mitigate this issue. We recommend using at least 0.016” or larger radii and maintaining uniform wall thickness by using outside and inside corner radii that share the same center point.

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An extrusion design with excessive hollows compared to an optimal design.
An extrusion design with excessive hollows compared to an optimal design.
An extrusion design with excessive hollows compared to an optimal design.

An extrusion design with excessive hollows compared to an optimal design.

Hollows and Lumen

Pro Tip: Avoid hollows when possible, and do not design hollows within each other. Protrusions within hollows should be minimal and extend no more than the wall thickness.


Hollow sections within extrusion profiles are called lumen. Lumen are typically more challenging to produce and regulate specifications. As such, hollow features have looser tolerance bands than external features. Hollows may also require additional steps and tools, such as vacuum sizing and air pressure to keep the shape of the part during cooling, which can cause the price to increase. Generally, it is best to avoid hollow sections whenever possible.


If your design requires hollows or multi-lumen features, then keep the following in mind to make them more manageable:



  • Do not design a hollow inside of another hollow. The position of a nested cavity cannot be easily managed and can impact the surrounding features before the part has wholly cooled, causing an out-of-specification part.
  • Details and protrusions, such as legs within hollows, should be avoided as they are also difficult to control. They should be minimal and protrude no deeper than the wall thickness if required.

Tolerancing

Pro Tip: Avoid excessively tight tolerances and only apply tighter tolerances to critical features.


To hold tighter feature tolerances, specialized tooling and setups may be required, increasing costs and lead times. Try to design for standard manufacturing tolerances and apply tighter tolerances to features critical to form, fit, and function. Extruded thermoplastics react strongly to temperature, expanding and contracting with it. For this reason, maintaining tight length specifications can be particularly difficult. As extrusion length increases, so should the allowable tolerance. For more information on standard plastic extrusion tolerances, visit our manufacturing standards page.

Material Selection

Choosing a suitable material for your project is crucial to your extruded part’s overall functionality and longevity. In addition, the material can be a primary driver for manufacturability and cost. The first step to picking a plastic resin is determining what characteristics your part will require for its intended use and environment, as not all plastics perform equally. These characteristics may include the following:

  • Environmental resistance (temperature, UV rays, weather, etc.)
  • Rigidity / Flexibility
  • Impact resistance and strength
  • Chemical resistance (e.g., cleaning agents, gasoline, oil, etc.)
  • Physical appearance

You can keep costs low by avoiding more exotic, less common materials and picking one that is more common and meets your part’s end-use requirements. To help you understand the differences between the different plastic resins and make the right choice for your project, we’ve compiled the table below, which compares commonly available materials for plastic extrusion. Xometry’s experts can also help guide you to the most suitable material and filler selection for your project and answer any questions.

Plastic Extrusion Materials Comparison Table
Material NameHeat StabilityChemical ResistanceUV ResistanceRigidityCost
Material Name

ABS

Heat Stability

Fair

Chemical Resistance

Poor

UV Resistance

Poor

Rigidity

High

Cost

Medium

Material Name

PVC

Heat Stability

Poor

Chemical Resistance

Poor

UV Resistance

Poor

Rigidity

Varies

Cost

Medium

Material Name

Low Density Polyethylene (LDPE)

Heat Stability

Poor

Chemical Resistance

Good

UV Resistance

Poor

Rigidity

Poor

Cost

Low

Material Name

High Density Polyethylene (HDPE)

Heat Stability

Fair

Chemical Resistance

Good

UV Resistance

Fair

Rigidity

High

Cost

Low

Material Name

PETG

Heat Stability

Poor

Chemical Resistance

Excellent

UV Resistance

Good

Rigidity

Medium

Cost

Medium

Material Name

UHMW PE

Heat Stability

Poor

Chemical Resistance

Good

UV Resistance

Poor

Rigidity

Medium

Cost

Low

Material Name

Polypropylene (PP)

Heat Stability

Excellent

Chemical Resistance

Excellent

UV Resistance

Poor

Rigidity

High

Cost

Low

Material Name

Nylon

Heat Stability

Excellent

Chemical Resistance

Excellent

UV Resistance

Fair

Rigidity

High

Cost

High

Material Name

Polycarbonate (PC)

Heat Stability

Excellent

Chemical Resistance

Fair

UV Resistance

Excellent

Rigidity

High

Cost

High

Isometric illustration of the plastic extrusion process.
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Joel Schadegg - Xometry Contributor
Joel Schadegg
Hey, I’m Joel and I’ll be your guide for everything Xometry! From my time as an Additive Technician in our 3D printing facility to operating a team of case managers as a Business Unit Manager, I have made it my personal mission to help customers like you you get the most out of the Xometry Experience. Now, as a Technical Writer, I am here to help you by providing expert advice to help you excel and achieve success on your projects.