Plastic Resin Injection Molding: The Role of Glass-Filled Thermoplastics

Glass-filled Plastic Parts – Why They’re So Popular & What Risks They Present

When discussing thermoplastic injection molding, glass-filled plastic is commonly used to enhance part strength and rigidity.

Some of the most common glass-filled thermoplastic resins include:

While thermoplastics do have naturally-occurring mechanical properties that impart strength, durability, impact-resistance and other benefits within plastic molded parts, adding glass-filled plastic can help further reinforce the resin’s properties.

The one issue that can occur with glass-filled plastic parts in thermoplastic injection molding is increased brittleness due to significant improvements in the part’s strength and rigidity.

However, if the glass-filled plastic part does not need to withstand high impact stress and deflection, but rather only support weight, then it can be an ideal plastic resin for injection molding.

In addition, glass fill percentages can range quite a bit (typically 13% to 45%), which will affect the final part’s properties accordingly.

  • Uniform Wall Thickness
  • No Sharp, 90-degree Angles
  • Few Through Holes & Turns
  • Non-complex Geometries
  • Gate Location at the Long Axis of the Part

If you’re considering using a glass-filled resin in the plastic molding process, it’s important to note that adding a glass-filled resin adds strength, but also poses risks as glass fibers can potentially cause internal stresses and warping, as well as fill rate, cooling rate and shrink rate issues.


U.S. Plastic Molding Company Specializing in Engineered Resins

Plastic Molded Concepts is a U.S. plastic molding company that uniquely specializes in molding with engineered resins. We provide all-inclusive plastic molding services, including post-molding operations.

Whether you need to improve an existing product, transition a part from metal to plastic, or bring an entirely new product to market, we cater to a wide range of industries and application needs.

Our in-house Master Molders are technically-trained and certified in plastic mold design, analysis, optimization, troubleshooting and issue resolution relating to complex molding projects.

Take the first step to begin the injection molding design process with us by downloading our Plastic Injection Molding Design Considerations Checklist.


Related Resources


Check out our case studies to see how we handle the most complex molding projects!

Have questions about our process?

Contact us today