Published by pultrx, the export trading company of Henan Zhongsheng. This is a buyer planning guide; the manufacturer confirms project specifications in writing.
For the 80, 90 and 140 profile systems and the finished-unit collection, start with pultrx FRP windows and doors
The comparison in one table
| Criterion | Aluminum | Vinyl (uPVC) | Fiberglass (pultruded) |
|---|---|---|---|
| Frame conductivity | High; needs a thermal break. Frame U-factor about 0.50 to 1.0 | Low; frame U-factor about 0.30 to 0.50, lower with foam-filled cavities | Low; cavities can be insulated. No U-factor range published in the cited source |
| Thermal movement | Expands much more than glass; seals and sealant joints work harder | Expands more than glass; softens in heat, UV fades dark colors | Expands at a rate similar to glass, so glazing seals see little differential movement |
| Strength for large openings | High; thin sightlines on big units | Lowest; hollow chambers need steel reinforcement on large sashes | About eight times stronger than vinyl; thinner frames on large windows |
| Service life (published) | Up to about 20 years with upkeep; can corrode and dent | Up to about 40 years; UV and freeze-thaw can break seals | Up to about 50 years; fades under prolonged UV without a finish |
| Maintenance | Low; finish wear | Lowest; no painting | Low; paintable |
| Cost per unit (US, 2018) | US$400 to 1,200 | US$150 to 2,000 | US$400 to 1,400 |
The cost rows are US residential retail figures published in 2018 and are quoted to show relative position, not current project pricing. Project pricing for a profile system or a finished unit depends on size, glazing, hardware and quantity, and is stated on the quotation.
Conductivity: the frame is the thermal edge
Aluminum conducts heat so well that an unbroken aluminum frame can have a U-factor two to three times that of a vinyl or fiberglass frame of the same size. Commercial aluminum systems solve this with a thermal break, a polyamide or polyurethane strip that separates the inner and outer halves of the extrusion. Vinyl and fiberglass are poor conductors to begin with, and both can be made better by filling the hollow chambers with foam. Whole-window performance still depends mostly on the glazing, which is why the NFRC label on a certified product, not the frame material, is the number to compare. For a project in a region with a national rating scheme, ask for the certified whole-window value for the exact configuration offered.
Thermal movement: why fiberglass frames keep their seals
A frame that expands at a different rate from the glass it holds puts the glazing seal and the perimeter sealant through a cycle every day. Aluminum and vinyl both expand considerably more than glass. Pultruded fiberglass is mostly glass fiber in a resin matrix, so its expansion is close to that of the glass pane, which is the reason the ARCHITECT comparison singles it out for reduced seal failure. The same stability shows in the sash: a fiberglass sash does not bow in summer heat, so locks and weatherstrips keep their contact. Dark exterior colors, which make vinyl soften and warp, are practical on fiberglass with a suitable finish.
Strength: large openings and thin sightlines
Vinyl is the weakest of the three, which is why large vinyl sashes carry steel reinforcement in their chambers and why vinyl frames are the bulkiest. Aluminum is strong and allows the thinnest frames. Pultruded fiberglass sits between them in sightline but close to aluminum in stiffness for the sizes used in windows, so lift-and-slide doors, tall casements and curtain-wall-style units can be framed in fiberglass without the steel inserts vinyl needs. Confirm the maximum sash size the system is tested for; it is a property of the profile system and the hardware, not of the material alone.
Durability and appearance over time
All three materials outlast the glazing unit's seal if the window is made and installed well. The differences are in how they fail. Aluminum corrodes at cut edges and in coastal or industrial air unless anodized or powder-coated, and it dents. Vinyl chalks and fades under UV, becomes brittle in cold climates and can distort in dark colors. Fiberglass needs a UV-stable finish, usually a factory paint or gelcoat, after which it holds color and shape; the published life estimate of up to 50 years assumes that finish is maintained. For a project buyer the question is not which material lasts longest but which finish specification and warranty the supplier will put in writing.
Where each material fits
Aluminum or vinyl usually stays
- Curtain walls and storefronts where sightline and span drive the design: thermally broken aluminum.
- Low-budget residential replacement in mild climates: vinyl.
- Projects where a local fabricator network for the chosen system already exists and the energy target is modest.
Pultruded fiberglass is a strong candidate
- Cold or hot climates with a demanding whole-window U-factor target and large glazed areas.
- Coastal, industrial or high-UV sites where aluminum corrodes and vinyl fades.
- Dark exterior colors, tall casements, tilt-and-turn and lift-and-slide units where sash stiffness matters.
- Projects that want one supplier for frame profiles and finished units.
Specifying a pultruded fiberglass frame system
A pultruded window frame is a set of profiles: frame, sash, mullion, glazing bead and the gaskets and hardware that join them. pultrx offers three section-based systems, the 80 series at 80 mm frame depth, the 90 series at 90 mm and the 140 series at 140 mm for sliding doors, and a separate collection of eleven finished window and door families. Frame depth and opening arrangement are the starting point; dimensioned section drawings, the glazing configuration and the hardware list complete the specification. Thermal, acoustic and weather performance belong to the finished unit as tested, so ask for the test report for the configuration you intend to order rather than inferring it from the frame material or the series number.
- State the opening schedule: sizes, operating type, quantity and the glazing you need.
- Choose the supply route: profiles for a local fabricator, or finished units assembled and glazed by pultrx.
- Ask for section drawings for the chosen series and the maximum tested sash size for each operating type.
- Ask for the test evidence behind any U-value, air, water or wind figure quoted, and the finish and warranty terms.
- Confirm who supplies glass, hardware, installation and inspection in the quotation.
Sources and further reading
- ARCHITECT magazine: How to specify a window frame (Selin Ashaboglu, March 2018)
Frame U-factor ranges of about 0.50 to 1.0 for aluminum and 0.30 to 0.50 for vinyl and wood; fiberglass expands at a rate similar to glass and is about eight times stronger than vinyl; service life and per-unit cost ranges by material.
- NFRC: window energy performance ratings
The NFRC label reports whole-window U-factor and solar heat gain coefficient for a certified product; frame material alone does not establish a rating.
Questions buyers ask
- Are fiberglass windows better than vinyl?
- Fiberglass frames are stiffer, move less with temperature and hold dark colors; vinyl is cheaper and needs no painting. For large openings, hot or cold climates and long service, fiberglass usually wins; for low-cost replacement in mild climates, vinyl often does.
- Are fiberglass windows better than aluminum?
- Fiberglass conducts far less heat than aluminum and does not corrode, while aluminum allows thinner frames and larger spans. Thermally broken aluminum narrows the energy gap but does not close it.
- How much do fiberglass windows cost compared with vinyl?
- A 2018 US survey put fiberglass units at about US$400 to 1,400 each and vinyl at US$150 to 2,000, so the ranges overlap. Project pricing depends on size, glazing and quantity and is quoted per order.
- What are the disadvantages of fiberglass windows?
- Higher price than basic vinyl, fewer local fabricators in some markets, and the need for a UV-stable finish to keep color over the long published life.
- Does the frame material set the window's U-value?
- No. The glazing sets most of it. Compare certified whole-window values for the exact configuration, such as the NFRC label in North America.
- Can I buy fiberglass window profiles without finished units?
- Yes. pultrx supplies the 80, 90 and 140 series profile sets for local fabrication as well as finished windows and doors.
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