How Are Fiberglass Windows Made | Windows of Wisconsin

How Are Fiberglass Windows Made
How Are Fiberglass Windows Made


How are fiberglass windows made? When it comes to choosing windows for your home, fiberglass windows stand out for their exceptional strength, durability, and energy efficiency. But have you ever wondered how these high-performance windows are made? At Windows of Wisconsin, we pride ourselves on being experts in the window industry, and we’re here to provide you with an in-depth look at the fascinating process of making fiberglass windows.

The Advantages of Fiberglass Windows

Before diving into the manufacturing process, it’s important to understand why fiberglass windows are a popular choice among homeowners:

1. Durability

Fiberglass windows are incredibly strong and resistant to warping, cracking, and rotting. They can withstand extreme weather conditions, making them ideal for various climates.

2. Energy Efficiency

Fiberglass has excellent thermal properties, providing superior insulation. This helps to reduce energy consumption by maintaining a consistent indoor temperature, leading to lower heating and cooling costs.

3. Low Maintenance

Unlike wood, fiberglass doesn’t require frequent painting or staining. It’s resistant to pests and moisture, ensuring that the windows remain in great condition with minimal upkeep.

4. Aesthetic Versatility

Fiberglass windows can be molded into various shapes and sizes, allowing for a wide range of design options. They can also be painted to match any décor, providing both functionality and aesthetic appeal.

The Manufacturing Process of Fiberglass Windows

Step 1: Creating the Fiberglass Material

Raw Materials

The primary raw materials used in making fiberglass are silica sand, limestone, soda ash, and various additives. These materials are melted together at high temperatures to form a molten glass.

Extrusion Process

  1. Melting the Glass: The raw materials are fed into a furnace and heated to around 1700°C (3092°F) until they melt and form a molten glass.
  2. Forming Fibers: The molten glass is then passed through fine nozzles to create thin strands of glass fibers. These fibers are rapidly cooled and collected.
  3. Sizing and Bundling: The glass fibers are coated with a chemical binder known as sizing, which helps to protect the fibers and enhance their adhesive properties. The fibers are then bundled together to form continuous filaments.

Step 2: Pultrusion Process


In the pultrusion process, the fiberglass filaments are combined with resin to create strong, durable profiles used in window frames and sashes. The resin typically used is polyester, but other types such as vinyl ester or epoxy can also be used depending on the desired properties.

Pultrusion Machine

  1. Fiber Placement: The glass fibers are pulled through a resin bath where they are thoroughly saturated with the resin. This combination of fibers and resin is known as a composite.
  2. Shaping and Curing: The saturated fibers are then pulled through a heated die that shapes and cures the composite into the desired profile. The heat initiates a chemical reaction in the resin, causing it to harden and bond with the fibers.
  3. Cutting and Finishing: Once the composite profile has been cured, it is cut to the required lengths. The profiles are then finished and prepped for assembly into window frames.

Step 3: Assembly of Fiberglass Windows

Frame and Sash Construction

  1. Cutting Profiles: The cured fiberglass profiles are cut to specific lengths required for the window frames and sashes.
  2. Joining Profiles: The profiles are joined together using various methods such as mechanical fasteners, adhesives, or welding, depending on the design and manufacturer’s specifications.
  3. Reinforcement: In some cases, additional reinforcement materials such as metal or extra layers of fiberglass are added to the profiles to enhance strength and durability.


  1. Glass Selection: The glass panes used in fiberglass windows are selected based on factors such as energy efficiency, UV protection, and noise reduction. Double or triple glazing options are available to further improve insulation.
  2. Sealing: The glass panes are securely fitted into the frame using glazing beads and sealed with high-performance sealants to prevent air and water infiltration.

Hardware Installation

  1. Locks and Handles: High-quality hardware, including locks, handles, and hinges, is installed to ensure smooth operation and enhanced security.
  2. Weatherstripping: Weatherstripping is applied around the frame to improve insulation and prevent drafts.

Step 4: Quality Control

Quality control is a critical step in the manufacturing process to ensure that each fiberglass window meets the highest standards of performance and durability.


  1. Visual Inspection: Each window is visually inspected for any defects, such as cracks, warping, or imperfections in the finish.
  2. Dimensional Checks: Precise measurements are taken to ensure that the windows meet the specified dimensions and tolerances.

Performance Testing

  1. Water and Air Infiltration: Windows are tested for their ability to resist water and air infiltration under simulated weather conditions.
  2. Thermal Performance: The thermal properties of the windows are tested to ensure they meet energy efficiency standards.
  3. Structural Integrity: Windows are subjected to various stress tests to ensure they can withstand high winds and impacts.

Step 5: Finishing and Packaging

Painting and Coating

Fiberglass windows can be painted in a wide range of colors to match any aesthetic preference. High-quality paints and coatings are applied to ensure a durable, long-lasting finish.


The finished windows are carefully packaged to prevent damage during transportation. Protective materials such as foam, plastic wrap, and sturdy boxes are used to ensure the windows arrive in perfect condition.

Innovations in Fiberglass Window Manufacturing

Advanced Composite Materials

Research and development in advanced composite materials have led to the creation of even stronger and more energy-efficient fiberglass windows. These innovations include the use of high-performance resins and fibers that offer improved thermal and mechanical properties.

Automation and Precision Engineering

The integration of automation and precision engineering in the manufacturing process has resulted in higher quality and consistency. Automated cutting, shaping, and assembly machines ensure that each window is produced with exact specifications and minimal variation.

Sustainable Manufacturing Practices

Manufacturers are increasingly adopting sustainable practices to reduce the environmental impact of fiberglass window production. This includes using recycled materials, reducing waste, and implementing energy-efficient processes.

Choosing the Right Fiberglass Windows for Your Home

At Windows of Wisconsin, we understand that selecting the right windows for your home is a significant decision. Here are some key factors to consider when choosing fiberglass windows:

Energy Efficiency

Look for windows with high energy efficiency ratings, such as those with Low-E glass and gas fills between the panes. Energy Star certification is a good indicator of energy-efficient performance.

Design and Style

Consider the architectural style of your home and choose windows that complement its design. Fiberglass windows are available in various styles, including casement, double-hung, sliding, and picture windows.

Maintenance and Longevity

Choose windows that require minimal maintenance and are designed to last for many years. Fiberglass windows are known for their durability and low maintenance requirements.

Professional Installation

Proper installation is crucial for the performance and longevity of your windows. At Windows of Wisconsin, our experienced team provides expert installation services to ensure your windows are installed correctly and perform optimally.

Fiberglass windows are an excellent choice for homeowners seeking durable, energy-efficient, and aesthetically versatile window solutions. Understanding the manufacturing process highlights the advanced technology and craftsmanship that go into creating these high-performance windows.

At Windows of Wisconsin, we are committed to providing our customers with top-quality fiberglass windows and exceptional service. If you’re considering upgrading your windows, our team of experts is here to help you choose the best options for your home and ensure a seamless installation process.

For more information or to schedule a consultation, visit our website or call us at (920) 429-9119. Let Windows of Wisconsin be your trusted partner in enhancing your home’s value, comfort, and energy efficiency with our premium fiberglass windows.