Understanding Window Frame Materials

What Are Aluminum-Clad Windows?

Aluminum-clad windows feature wood interior frames protected by extruded aluminum exterior cladding. This dual-material construction combines wood's natural insulating properties and traditional aesthetic appeal on the interior with aluminum's exceptional weather resistance and durability on the exterior.

The extruded aluminum cladding protects interior wood components from moisture exposure, UV radiation, and temperature extremes while requiring minimal exterior maintenance. Factory-applied finishes on aluminum cladding resist fading, chalking, and weathering, eliminating painting or refinishing requirements that exposed wood exteriors demand.

What Are Fiberglass Frame Windows?

Fiberglass windows use pultruded fiberglass composite materials for both interior and exterior frame components. This single-material construction provides consistent properties throughout the frame, with fiberglass offering low thermal conductivity, high strength-to-weight ratios, and dimensional stability across wide temperature ranges.

Fiberglass frames resist warping, swelling, and moisture-related deterioration while maintaining structural integrity in extreme conditions. The material expands and contracts at rates similar to glass, helping maintain tight seals and reducing stress on glazing systems during temperature fluctuations.

Colorado's Unique Climate Challenges

High-Altitude UV Intensity

Colorado's elevation increases UV exposure compared to sea-level locations, accelerating degradation for materials lacking adequate UV resistance. Window frames must withstand this increased UV intensity throughout their service life without significant fading, chalking, or structural deterioration.

Both fiberglass and aluminum-clad frames resist UV degradation substantially better than vinyl alternatives that can become brittle or discolored under intense UV exposure. However, finish quality, UV stabilizers, and protective coatings affect long-term appearance retention and performance maintenance for both materials.

Temperature Extremes and Daily Swings

Colorado's climate creates dramatic daily temperature variations throughout the year. Summer days reach 90°F+ followed by cool nights dropping to 50°F, while winter conditions swing from sunny 50°F afternoons to overnight temperatures well below 0°F. These temperature cycles stress window frames through repeated expansion and contraction.

Frame materials with thermal expansion rates closely matching glass minimize stress on seals and glazing systems during temperature changes. Materials expanding significantly differently than glass can create gaps, seal failures, or stress that compromises long-term performance and energy efficiency.

Occasional Hail Events

Colorado's hail season presents periodic impact risks that can damage window frames and affect overall window integrity. Frame materials must withstand occasional hail impacts without denting, cracking, or permanent deformation that compromises window function, weather-tightness, or appearance.

Material Performance in Colorado Conditions

Thermal Insulation Properties

Fiberglass provides superior thermal insulation compared to aluminum due to fundamental material composition differences. Fiberglass's low thermal conductivity helps prevent heat transfer through frame sections, improving overall window energy performance. Aluminum conducts heat readily, though quality aluminum-clad construction incorporates thermal breaks and insulating wood interior components to address this characteristic.

The thermal performance difference proves most significant for windows with substantial frame area relative to glass area. For typical residential windows with relatively narrow frames and large glazing areas, Low-E glass selection and proper installation often affect energy performance more than frame material choice alone. Always verify NFRC labels comparing complete window assemblies rather than evaluating frame materials in isolation.

Dimensional Stability Across Temperature Ranges

Fiberglass frames expand and contract at rates very similar to glass, providing exceptional dimensional stability across Colorado's wide temperature ranges. This stability helps maintain tight seals between frames and glazing, preventing air infiltration or moisture penetration that compromises performance and comfort.

Aluminum expands at different rates than glass, requiring careful engineering to accommodate thermal movement without creating gaps or seal stress. The wood interior component in aluminum-clad windows also responds to moisture and temperature changes, adding complexity to dimensional stability considerations. Quality aluminum-clad products account for these factors through proper design and construction techniques.

Structural Strength and Rigidity

Both fiberglass and aluminum offer excellent structural strength for residential window applications. Fiberglass provides high strength-to-weight ratios, allowing narrow frame profiles while maintaining structural integrity for large window sizes. The material resists bending and flexing under wind loads and operational stresses.

Aluminum's inherent strength allows thin exterior cladding that protects wood interiors without adding excessive weight or bulk. The combination of aluminum cladding with wood interior structure creates robust assemblies handling typical residential window loads effectively.

UV Resistance and Color Retention

Both materials resist UV-related degradation substantially better than vinyl alternatives. Aluminum cladding with quality factory-applied finishes maintains color and appearance for decades under Colorado's intense UV exposure. Protective coatings on aluminum surfaces resist fading, chalking, and weathering.

Fiberglass frames with proper UV stabilizers and quality finishes also resist sun-related deterioration and discoloration. The material itself remains structurally sound under UV exposure, with finish longevity depending on coating quality and application processes.

Moisture Resistance

Aluminum cladding provides exceptional protection against moisture penetration, shielding interior wood components from rain, snow, and humidity exposure that would otherwise cause deterioration. The non-porous aluminum surface prevents water absorption while factory-sealed joints minimize moisture entry points.

Fiberglass frames resist moisture absorption throughout the material, eliminating concerns about swelling, warping, or rot that affect exposed wood. The material maintains dimensional stability and structural integrity even in high-humidity conditions or direct water exposure.

Impact Resistance and Hail Performance

Aluminum cladding can dent from severe hail impacts, though dents typically represent cosmetic rather than functional damage. Windows continue operating properly despite surface denting, with weather-tightness and performance generally unaffected by moderate hail damage.

Fiberglass frames resist denting better than aluminum in many applications, though severe impacts can crack or chip fiberglass surfaces. The practical difference for typical Colorado hail events remains modest, as severe storms damaging window frames also affect glass, roofing, and other building components regardless of frame material.



Maintenance and Longevity

Maintenance Requirements

Both materials require minimal maintenance compared to exposed wood or vinyl alternatives. Aluminum-clad windows need only periodic cleaning, with factory-applied finishes eliminating painting or refinishing requirements. The durable coatings resist environmental degradation while maintaining appearance for decades.

Fiberglass frames similarly require only routine cleaning without refinishing, repainting, or special treatments. Quality factory finishes resist weathering, UV exposure, and normal wear while maintaining original appearance throughout window service life.

Expected Service Life

Both materials provide excellent longevity for Colorado applications when properly manufactured and installed. Aluminum cladding protects interior wood components from weather exposure, allowing decades of reliable service. The non-corrosive properties of aluminum ensure continued protection and performance over extended periods.



Fiberglass frames maintain structural integrity and appearance throughout their service life without degradation from moisture, temperature cycling, or UV exposure. The material's inherent stability contributes to sustained performance matching or exceeding aluminum-clad alternatives.

Aesthetic Considerations

Interior Appearance Options

Aluminum-clad windows provide natural wood interiors for homeowners wanting traditional wood aesthetics on the room side. This flexibility allows staining or painting interior surfaces to match existing trim, cabinetry, and décor preferences. Wood species selection and finish options accommodate various design styles from traditional to contemporary.

Fiberglass frames typically feature consistent appearance inside and outside, though some products offer woodgrain finishes replicating wood appearance. The uniform material simplifies color coordination while providing contemporary aesthetics that complement modern home designs.

Exterior Design Flexibility

Aluminum cladding offers extensive color options from standard palettes to custom colors matching specific design requirements. The durable factory-applied finishes maintain color consistency across multiple windows while resisting fading and weathering.

Fiberglass exteriors provide color options through factory-applied finishes, typically with more limited palette selections than aluminum-clad alternatives. The finish durability and weather resistance support long-term appearance retention in Colorado's challenging climate.

Frame Profile and Sightlines

Fiberglass's high strength-to-weight ratio allows narrow frame profiles that maximize glass area and views. The material maintains structural integrity even with minimal frame width, creating contemporary aesthetics with emphasis on glazing rather than frames.

Aluminum-clad construction typically features slightly wider frame profiles accommodating wood interior components and aluminum exterior cladding. The additional width remains modest for quality products, with overall appearance depending more on design details than fundamental material differences.

Cost Considerations

Initial Investment Comparison

Aluminum-clad windows typically cost more than fiberglass alternatives due to dual-material construction combining wood interiors with aluminum cladding. The premium reflects material costs, manufacturing complexity, and aesthetic flexibility of natural wood interiors.

Fiberglass windows generally represent mid-range pricing between vinyl and premium aluminum-clad products. Single-material construction simplifies manufacturing while delivering excellent performance characteristics and durability.



Long-Term Value Assessment

Both materials offer strong long-term value through durability and minimal maintenance requirements. The initial cost difference becomes less significant when evaluated over complete window service life spanning multiple decades.

Focus on total value including performance characteristics, aesthetic satisfaction, maintenance expectations, and durability rather than initial price alone when selecting frame materials for long-term home investments. Quality products from either material category provide excellent value over extended service periods.

Making the Right Material Choice

When Aluminum-Clad Windows Excel

Consider aluminum-clad windows when:

●  Natural wood interior aesthetics represent important design priorities

●  Matching existing wood trim and architectural details proves essential

●  Traditional or historic home styles benefit from authentic wood appearance

●  Extensive exterior color customization options are desired

●  Budget accommodates premium window investments

When Fiberglass Windows Excel

Consider fiberglass windows when:

●  Maximum thermal insulation performance matters most

●  Contemporary aesthetics with narrow frame profiles appeal

●  Dimensional stability across extreme temperature ranges is prioritized

●  Lower maintenance and consistent interior/exterior appearance preferred

●  Budget-conscious selections without compromising quality and durability

Climate-Specific Considerations for Colorado

Both materials perform well in Colorado's challenging climate when properly specified and installed. The intense UV exposure, dramatic temperature swings, and occasional hail affect both materials similarly, with quality products handling Colorado conditions effectively throughout their service lives.

Focus on complete window specifications including Low-E glass packages, proper sizing, NFRC performance ratings, and professional installation rather than frame material alone. These factors affect long-term performance, comfort, and energy efficiency as much or more than frame material selection for most residential applications.

At Five Seasons Windows & Doors, we specialize in premium aluminum-clad windows from Marvin's Signature® Ultimate collection. While understanding different frame materials helps homeowners make informed decisions, we've chosen to focus our expertise on aluminum-clad construction for its combination of wood interior beauty, weather-resistant aluminum protection, and proven performance in Colorado's demanding climate. Contact us to discuss how our aluminum-clad window solutions can meet your specific needs.

People Also Ask About Fiberglass vs Aluminum Windows

1. Which window frame material lasts longer in Colorado's climate?

Both fiberglass and aluminum-clad windows provide decades of service in Colorado when properly manufactured and installed. Aluminum cladding protects interior wood from weather exposure while fiberglass frames resist moisture and temperature effects throughout. Expected service life depends more on product quality, proper installation, and maintenance than frame material choice alone.

Quality products from reputable manufacturers offer extensive warranties reflecting confidence in long-term durability. Evaluate complete window specifications, NFRC performance ratings, and manufacturer reputation rather than focusing solely on frame material when assessing longevity for Colorado applications.

2. Are fiberglass windows more energy efficient than aluminum-clad?

Fiberglass frames provide better thermal insulation than aluminum due to lower thermal conductivity. However, complete window energy performance depends primarily on Low-E glass packages, proper installation, and overall construction quality rather than frame material alone. Quality aluminum-clad windows with thermal breaks and premium glazing achieve excellent energy performance approaching fiberglass alternatives.

Always verify NFRC labels for specific products comparing U-factor and Solar Heat Gain Coefficient values. These standardized ratings reflect complete window assembly performance including frames, glass, and spacers rather than frame materials in isolation.

3. Do aluminum-clad windows dent easily from Colorado hail?

Aluminum cladding can dent from severe hail impacts, though most residential hail events cause minimal or no frame damage. When denting occurs, it typically represents cosmetic rather than functional damage, with windows continuing to operate properly and maintain weather-tightness. Severe hail damaging aluminum cladding typically also breaks glass and damages roofing regardless of frame material.

Hail resistance concerns apply more to glass and roofing than window frames for most Colorado applications. Proper insurance coverage addresses hail damage risks more effectively than frame material selection for protecting homes from occasional severe weather.

4. Can you paint or refinish fiberglass window frames?

Fiberglass frames feature durable factory-applied finishes designed for long-term performance without refinishing requirements. While fiberglass technically accepts paint, the weather-resistant factory finishes eliminate practical needs for repainting. Attempting to paint fiberglass frames may void warranties and compromise factory finish durability.

Aluminum-clad windows with wood interiors allow interior refinishing or restaining to accommodate changing décor preferences. This flexibility benefits homeowners wanting to update interior appearance without window replacement.

5. Which frame material requires less maintenance in Colorado?

Both fiberglass and aluminum-clad windows require minimal maintenance in Colorado's climate. Aluminum cladding protects interior wood from weather exposure, with durable factory finishes resisting fading and weathering without painting. Fiberglass frames similarly require only periodic cleaning without refinishing, repainting, or special care.

Maintenance requirements depend more on product quality and installation than frame material. Both materials substantially reduce maintenance compared to exposed wood or vinyl alternatives requiring refinishing or replacement due to Colorado's UV exposure and temperature extremes.

Related Reading

Regardless of frame material selection, glass coating technology significantly impacts window performance in Colorado's high-altitude environment. Low-E coatings manage heat transfer and UV transmission while maintaining natural light and views, providing benefits that complement quality frame materials.

Understanding how Low-E coatings work with different frame materials helps optimize overall window performance for Colorado conditions. The coating technology delivers energy savings, UV protection for furnishings, and improved comfort through consistent glass surface temperatures. These benefits apply whether windows feature fiberglass frames, aluminum-clad construction, or other frame materials.

For comprehensive information on Low-E coating technology, performance benefits, and how these coatings enhance window efficiency regardless of frame choice, see our detailed guide on Low-E coated glass benefits for energy savings and UV protection.



Our Take

At Five Seasons Windows & Doors, we specialize in premium aluminum-clad window products from Marvin's Signature® Ultimate collection, which excel in Colorado's demanding climate. Our experience throughout Colorado shows that quality aluminum-clad construction handles the state's intense UV exposure, temperature extremes, and weather conditions exceptionally well when combined with appropriate Low-E glass packages and professional installation.

While this article provides educational comparison of frame materials to help homeowners understand their options, we focus on delivering proven aluminum-clad solutions that combine wood interior beauty with weather-resistant aluminum protection. We help clients evaluate complete window specifications from our product lines matching their homes, performance priorities, and budgets while ensuring selections perform reliably throughout Colorado's challenging conditions.



Final Takeaway

Fiberglass and aluminum-clad windows both perform well in Colorado's challenging climate, with material selection depending on aesthetic preferences, thermal performance priorities, and budget considerations rather than absolute superiority of either option. Aluminum-clad windows provide traditional wood interior beauty with weather-resistant aluminum protection, while fiberglass offers superior thermal insulation and dimensional stability in single-material construction.



Colorado's high-altitude UV exposure, temperature extremes, and occasional hail affect both materials similarly when quality products are properly installed. Focus on complete window specifications including Low-E glass packages, NFRC performance ratings, proper sizing, and professional installation rather than frame material alone. Understanding how each material responds to Colorado's conditions helps homeowners make informed decisions delivering decades of reliable performance.

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