Two windows can look identical on the drawings and behave very differently in year fifteen. That is the real wood vs fiberglass question: not which material is "better," but which one you are willing to live with once the warranty paperwork is in a drawer.
Short answer: wood gives you the warmest interior and the most design freedom, and it asks for a coating schedule on the weather side. Fiberglass asks for less, and gives up the look of real timber on the inside unless it is a wood-interior hybrid. If you want wood inside and little upkeep outside, the third option is aluminum-clad wood.
One disclosure first. I source European wood, aluminum-clad wood, aluminum and uPVC windows. I do not sell fiberglass frames, so treat this as a buyer's guide from someone with no fiberglass to push - and who will tell you when fiberglass is the better call.
What You Are Actually Comparing
Wood windows are timber frames and sashes with a factory finish. The European ones I quote are laminated from several glued layers rather than cut from one board, impregnated before machining, and lacquered in the plant. The details are in wood window frames explained.
Fiberglass windows are frames made from glass fibers and resin, usually with a painted or coated finish. Brands differ in what goes inside and outside: Marvin's Elevate pairs a pine interior with an Ultrex fiberglass exterior (marvin.com, read October 2026), and Andersen's A-Series is a wood interior with a fiberglass and composite exterior. So "fiberglass window" can mean an all-fiberglass frame or a wood-inside hybrid. Ask which one is in your quote.
Side by Side
| Item | Wood | Fiberglass |
|---|---|---|
| Interior look | Real timber, any species or color | Painted fiberglass, or real wood in a wood-interior hybrid |
| Exterior upkeep | Recoat the weather side from time to time | Generally lower; a painted finish still ages |
| Dimensional stability | Good when laminated and sealed | Dimensionally stable |
| Frame insulation | Wood insulates relatively well | Hollow cavities can be filled with insulation |
| Repair | Sand and refinish, replace a rail | Depends on the maker; ask what a damaged finish costs to fix |
| Typical fit | Interiors where timber is the point | Exposed, low-maintenance elevations |
The U.S. Department of Energy's window guidance says wood frames insulate relatively well but need regular maintenance, and that fiberglass frames are dimensionally stable with cavities that can be filled with insulation (energy.gov, Window Types and Technologies, read October 2026). It also makes a point worth keeping: for energy performance, the glazing decision usually matters more than the frame material.
Maintenance: The Honest Difference
A good wood window does not wear out; its coating does. Water sitting on bare end grain is what shortens a wood window's life, so the weather side gets a light sand and a fresh coat when it dulls - often in the 5-10 year range on exposed elevations. I lay out the full schedule in how long do wood windows last.
Fiberglass takes most of that off your list. It is not timber, so there is no end grain to rot, and it is generally sold with little or no routine recoating. The catch: a painted fiberglass finish is still a finish, so ask the maker what the finish warranty covers and how a damaged area is repaired.
If you know nobody will ever get a ladder to the third-story wall, that decides it - for fiberglass or for aluminum-clad wood.
Looks and Sightlines
Wood wins inside. A laminated pine, meranti or oak sash can be stained to show the grain or painted in any opaque color, and you can change your mind later with a new coat. See the species in pine, meranti, oak or larch.
Outside, if thin sightlines drive the design, look at Clad Flush or the aluminum-clad wood windows page: an extruded aluminum shell over a timber core, in any RAL color.
Where Fiberglass Wins
- Exposed elevations where recoating is a real cost, such as tall stairwell glass or hard-to-reach walls.
- Rentals and spec work where nobody will maintain a finish.
- Budgets that need a stable, low-upkeep frame and do not need timber inside.
I would not argue a client out of fiberglass in those cases.
Where Wood Wins
- Interiors where timber is the design - paneled rooms, historic districts, a client who wants the grain.
- Repairability. A scratched wood sash is a sanding job.
- Design freedom in species, color and profile, including the rounded profiles of Timber Classic and the deeper Timber Estate.
The Middle Road: Aluminum-Clad Wood
Aluminum-clad wood keeps the timber interior and moves the maintenance problem outside. The aluminum shell is clipped on over a ventilated gap, so it sheds weather while the wood stays out of the rain and UV. For many clients who ask me "wood or fiberglass," this is the answer: wood they can see, a powder-coated shell they do not have to repaint. DOE notes that cladding reduces wood's maintenance. The comparison against bare wood and full aluminum is in aluclad vs aluminum vs wood windows.
What I Would Choose
- Timber is the point of the room: wood, with a plan for the recoat.
- Wood inside, little upkeep outside: aluminum-clad wood.
- Exposed wall, no timber needed, no maintenance wanted: from my range, aluminum or uPVC; fiberglass if that is the product you prefer.
Send me the elevations and I will say which of the wood and clad options fit. Wood and aluminum-clad wood are quoted from drawings; the estimator gives a first idea for aluminum and uPVC.
FAQ
Are fiberglass windows better than wood? Better at low maintenance, not at everything. Fiberglass is dimensionally stable and needs less upkeep outside; wood gives real timber inside and can be refinished and repaired.
Do fiberglass windows last longer than wood? It depends on upkeep. A wood window with a maintained coating can last decades, and the coating, not the timber, is what ends its life. Fiberglass removes the recoat step, so it is more forgiving of neglect.
Are fiberglass windows more energy efficient than wood? Frames of both materials can perform well. The glazing usually matters more than the frame, so compare whole-window U-factor and SHGC for the sizes and glass you are actually buying.
Can you get a wood interior with a low-maintenance exterior? Yes. Aluminum-clad wood puts a powder-coated aluminum shell over a timber frame, and some fiberglass lines also offer wood interiors.
Do you sell fiberglass windows? No. I source European aluminum, wood, aluminum-clad wood and uPVC windows. This guide is meant to help you choose the right material, even when it is not one I sell.