Before anything else: in Washington, how a window is installed matters more than what its frame is made of. A mid-range window with proper flashing and a sill pan will outlast a premium window installed without them.
That said, frame material is a real decision with real consequences.
Vinyl
The most common choice across Washington and the most affordable. It does not rot, does not need painting, and copes well with the marine climate west of the Cascades, which is why it dominates in Puget Sound.
The limitations are worth knowing. Vinyl expands and contracts more with temperature change than other materials, which matters more in Eastern Washington’s wide seasonal range than in the marine west. Colour options are limited compared with materials that can be painted, and darker colours absorb more heat.
Quality varies considerably within vinyl. Frame construction, welded versus mechanically fastened corners, and reinforcement in larger units all differ between products that look similar.
Fiberglass
More expensive than vinyl and more dimensionally stable across temperature swings. Its expansion rate is closer to glass, which reduces stress on the seal over years of thermal cycling.
That stability is a stronger argument in Spokane, Yakima and the Tri-Cities, where a window can face genuine summer heat and genuine winter cold within the same year, than it is in the narrow temperature band of the marine west.
It can also be painted, which matters where appearance or colour matching is a consideration.
Wood
The appearance argument, and in the right house it is a real one. Period properties and homes in areas with design review sometimes require it, and nothing else quite matches it visually.
The honest trade-off in Washington is maintenance. Wood in a marine climate needs its finish maintained, and neglected wood windows rot. That is not a theoretical risk here — it is the reason so many older Washington homes are replacing wood windows now.
Clad wood — a wood interior with an aluminium or fiberglass exterior — addresses much of this, giving the interior appearance without exposing timber to persistent damp. It costs more accordingly.
Aluminium
Common in older Washington homes and rarely specified for residential replacement now, because bare aluminium conducts heat readily and produces condensation. Thermally broken versions perform far better but sit at a higher price point.
If you have single-pane aluminium windows from the 1960s or 1970s, they are almost certainly the worst-performing element of your building envelope.
What to weigh
Which side of the Cascades. Marine west favours vinyl’s cost advantage; the wider eastern temperature range favours fiberglass’s stability.
How long you are staying. Material longevity differences play out over decades.
Appearance requirements. Design review or a period property may narrow the options.
Maintenance appetite. Be honest. Wood windows that will not get maintained will not last, and there is no shame in choosing something that does not depend on you.
The thing to prioritise
If your budget forces a choice between a better frame material and a better installation, choose the installation. Water getting into a wall around a premium window is a considerably worse outcome than a mid-range frame properly flashed.