What’s the Difference Between Vinyl and Fiberglass Windows?

Vinyl vs. Fiberglass Windows: A Side-by-Side Comparison

Updated July 6, 2025

Learn the key differences between vinyl and fiberglass replacement windows, including durability, energy performance, cost, and long-term value—backed by over 50+ years of installation experience in Colorado.

Overview

Choosing the right window material impacts your home’s comfort, value, and energy savings. At Gravina’s Window Center of Littleton®, we specialize in premium fiberglass windows from Infinity from Marvin®, a top-tier option built for Colorado's extreme climate. Below, we break down how fiberglass compares to traditional vinyl.

Durability in Colorado Weather

Colorado’s climate puts windows to the test. High-altitude UV exposure, temperature swings, and heavy snowfall demand materials that won’t warp or crack.

  • Vinyl resists rot and rust but expands and contracts with heat. This movement can lead to seal failure and frame warping.
  • Fiberglass, especially Ultrex®, maintains stability across temperature changes. It’s engineered to be 8x stronger than vinyl, resisting flex and ensuring long-term performance.

Energy Efficiency

Heat loss through windows can account for up to 30% of your home’s energy bill. Frame material and glass coatings make a measurable difference.

  • Vinyl is often ENERGY STAR® certified but may lose performance over time if seals fail or frames warp.
  • Fiberglass has a low thermal expansion rate. Combined with Low-E glass, it keeps heat in during winter and out during summer.

View ENERGY STAR criteria

Cost Comparison

Vinyl windows are generally cheaper upfront but may need replacement after 10–15 years. Fiberglass costs more initially but can last 30+ years with little maintenance.

  • Vinyl has a lower price point but a shorter lifespan.
  • Fiberglass costs about 15–30% more but delivers better value over time. See the 2024 Cost vs. Value Report

Design & Aesthetic Flexibility

  • Vinyl comes in preset factory colors and can’t be painted. Its thicker frames reduce visible glass area.
  • Fiberglass allows slimmer profiles for more daylight and can be painted to match your home’s style.

Environmental Impact

  • Vinyl is petroleum-based and not widely recyclable.
  • Fiberglass is made from natural materials like silica sand and often includes recycled content. Its long lifespan also reduces waste.

Side-by-Side Comparison: Vinyl vs. Fiberglass Windows

FeatureVinylFiberglass (Ultrex®)
Expected Lifespan10–15 years30+ years
Thermal ExpansionHigher rate; may cause seal failureVery low rate; maintains seals
Frame ProfileThicker; less glass areaSlimmer; more visible glass
PaintableNoYes
SustainabilityPetroleum-based; not recyclableSilica-based; long lifespan

Why We Recommend Infinity from Marvin®

At Gravina’s Window Center of Littleton®, we install Infinity from Marvin® fiberglass windows because they perform in Colorado’s climate. Every unit is installed by Marvin-certified technicians and backed by our lifetime labor warranty.

Have questions? Schedule your free consultation or visit our showroom.

About the Author: Jim Gravina is the founder of Gravina’s Window Center of Littleton®, a Infinity-authorized retailer serving Colorado since 1973. Learn more.

4 Comments

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