Seattle Fiberglass Windows

Fiberglass windows consist of strands of extremely fine glass fibers made from silica sand, limestone, and soda ash. These strands are woven together, pulled through a resin bath, and then placed in a heated die to cure. Fiberglass frames have air cavities that can be filled with foam or a hollow core, providing excellent insulation, while the frame expands and contracts at the same rate as the glass window pane it holds. This minimized expansion and contraction reduces air leakage, making fiberglass the greatest window material for Seattle homeowners who value energy efficiency.

Top Fiberglass Window Benefits

  • Fiberglass windows provide the highest level of energy efficiency available.
  • Fiberglass is extremely durable, with a lifespan of 50-80 years.
  • Fiberglass is extremely difficult to damage and doesn’t warp, crack, or rust.
  • These windows are available in various styles and colors, perfect for any home design.
  • Fiberglass is environmentally friendly and a great choice for eco-conscious homeowners.

The Finest Fiberglass Manufacturer Chosen For You

Let us use our experience and industry knowledge to your benefit. With over 30 years in the window industry, time has allowed us to determine the fiberglass manufacturer that delivers you the best blend of quality, price, and VALUE. Our chosen manufacturer partner creates value in four essential areas: consistency of quality and service over the years, level of warranty support to you, industry longevity, and product innovation.

At Lake Washington Windows and Doors, our valued manufacturer partner for fiberglass windows is:

The Milgard Ultra Series fiberglass windows are top-of-the-line when it comes to window technology. Fiberglass is an eco-friendly window material that provides the highest energy-efficiency levels available. Fiberglass is made primarily of silica sand, an abundant natural resource. Glass is made primarily of sand. Thus the frame and glass expand and contract at roughly the same rate while remaining resistant to swelling, rotting, and warping, allowing for a longer lifespan.

Features and Benefits:

  • Extremely durable with an expected lifespan of nearly 80 years.

  • Strong frame material allows for large custom sizes

  • Paintable frames that homeowners can update to match current home color trends

  • Low expansion/contraction rate through 100-degree temperature changes means less glass and caulking failure over time

  •  An Energy Star package tailored to the Seattle region for optimal energy efficiency.

  •  Custom colors, hardware, and glass options to match any home design.


Milgard Ultra Series C650 Fiberglass Windows

Window Configurations Combinations Hardware Features Color Options Grid Options Glass Textures Tint Options Screen Options
Picture window
Picture window 2-lites verticle
Picture window 2-lites horizontal
Picture window 3-lites verticle
Picture window gable
Picture window 3-lites horizontal
Picture window gable triangle
Picture window hexagon
Picture window octagon
Gable (3-side, 4-side, 5-side)
4-sided gable and square picture windows
Picture window over awning
4-sided gable windows over picture windows
Folding Nesting Operator
Sash locks
Interior Colors
White (any exterior color)
Harmony (harmony exterior only
Bark (bark exterior only)
Black bean (black bean exterior only)

Exterior Colors
Black bean

Interior Grids
Flat GBG Grid
Sculptured GBG Grid
3/4″ Vintage SDL
1-1/8″ Vintage SDL
1-1/8″ Craftsman SDL
1-1/8″ Legacy SDL

Exterior Grids
Flat GBG Grid
Sculptured GBG Grid
3/4″ Vintage SDL
1-1/8″ Vintage SDL
1-1/8″ Craftsman SDL
1-1/8″ Legacy SDL

Obscure Aquatex
Obscure Clear 42
Obscure Delta Frost
Obscure Frosted Glue Chip
Obscure Glue Chip
Obscure Matelux
Obscure Narrow Reed
Obscure P516
Obscure Rain
Cardinal Low-E
Solar Bronze
Solar Gray
Standard Mesh
PureView Mesh
Milgard Ultra Series C650 Fiberglass Picture Window Size Chart

Comparing Fiberglass to Vinyl and Clad-Wood Windows

Compared to other window materials, we consider fiberglass the highest quality material available for your Seattle home. It provides optimal levels of performance and durability, along with many design options.

While fiberglass is more energy-efficient and durable than vinyl window materials, it’s also significantly more expensive. Because of this, we recommend fiberglass windows to homeowners who want the best material money can buy and vinyl windows for homeowners who desire comparable performance at a more affordable price.

When deciding between fiberglass and clad-wood windows, the decision boils down to your design preference. While fiberglass outperforms vinyl clad-wood windows, they are better suited for modern home designs, whereas clad-wood windows are an excellent choice for traditional home designs.

Fiberglass Window Frames Available in a Range of Styles

It doesn’t matter what window style you’re looking for. At Lake Washington Windows and Doors, we offer vinyl replacement window options in 6 of the 7 primary home window styles, including


Milgard Ultra Series Milgard Tuscany Series Milgard Trinsic Series Andersen E-Series
Frame Material Fiberglass Vinyl Vinyl Aluminum Clad Wood
Strength Excellent Excellent Very Good Excellent
Durability Excellent Very Good Very Good Very Good
Large Size & Custom Designs Excellent Very Good Good Excellent
Energy Efficiency Excellent Excellent Excellent Excellent
% Glass to Frame



Very Good Excellent Very Good
Curb Appeal Excellent Excellent Excellent Very Good
Exterior Colors 6 7 7 50
Warranty Excellent Excellent Excellent Very Good
Price $$$$ $$$ $$ $$$$


Top-Rated Window Replacement Services

At Lake Washington Windows and Doors, we offer the highest quality windows and unparalleled customer service, with over 800 5-star reviews. With each installation, our exclusive Leak Armor Installation provides superior protection around your window openings. When you choose us for your window installation project, you can be sure that you’re getting the best.

Financing Options with Convenient 10 Minute Approvals   

In addition to special offers and promotions, ask  our sales representative about our quick, digital financing application process.  From low-interest traditional loans to no down-no payment-no interest deferred financing plans,  we can help you fund your replacement window project so you can mobilize your cash for other investments.  We are a proud partner of GreenSky, one of the largest lenders for the home improvement industry.   See how much you can be pre-approved for.  

Every Window Includes a Limited Lifetime Warranty

The beauty of working with the top window manufacturers in the industry is the support you can expect before, during, and after installation. Both Milgard and Andersen offer limited lifetime warranties. However, the likelihood that you’ll need to take advantage of these warranties is low.

Milgard Lifetime Warranty Guarantee

Milgard’s award-winning windows and doors are built to last. However, if you ever encounter an unexpected problem, you can rest assured that their lifetime warranties cover your purchase.

Andersen Limited Lifetime Warranty Guarantee

Andersen prides itself on crafting durable, long-lasting products. That resilience allows them to offer some of the best warranties in the industry. They're even transferable should you sell your home. With Andersen’s exclusive Owner-to-Owner® limited warranties, you get peace of mind plus real added value.

Receive Our Patented Leak Armor Protection with Every Installation

We include our patented Leak Armor protection with every window we install. Developed through thousands of customer installations and years of experience, we utilize layers of flashing, pans, and sealants in a specific manner to provide commercial-grade sealing to residential homes.

Fiberglass Window FAQs

Are Fiberglass Windows worth it?

The popularity of fiberglass windows is higher than ever. While the upfront cost is more significant, fiberglass provides benefits that vinyl windows do not. If you’re willing to spend the money upfront and reap the return on investment over time, then fiberglass windows are a worthwhile option for you and your home. 

What style and color options are available with fiberglass windows?

Fiberglass is a versatile window frame material that can be molded and configured into most window styles. Milgard offers a range of interior and exterior colors, along with several different glass textures and window grids. Visit our window style page to explore the fiberglass options we provide.

Are fiberglass replacement windows durable?

Fiberglass windows do not damage easily. They will resist dents, scratches, warping, rotting, and corroding. The material is also strong and rigid, allowing fiberglass windows to be up to eight times stronger than vinyl windows and requiring much less maintenance.

How long does the fiberglass window installation process take?

At Lake Washington Windows and Doors, our installation process is down to a science. When embarking on a project with new customers, we generally schedule 2-5 days for installation, depending on the project size.