Sauna wood is not a decorative choice, it is a functional one, and the reasons some species are used and others are never used inside a hot room are physical rather than aesthetic. The lining has to stay cool enough to touch at high temperature, resist repeated heating and drying without splitting, and not release resin or a strong smell when hot. That rules out a great deal of ordinary construction timber before any question of looks arises.
Why some woods are ruled out
Pine and spruce with visible knots are the usual mistake. Resinous softwoods weep sap when hot, and a bead of hot resin on a bench is a genuine burn risk as well as a mess. Dense hardwoods such as oak are a different problem: they conduct heat well, so a bench made from them becomes painful to sit on at sauna temperatures. Anything treated, painted or glued with adhesives not rated for heat is out entirely, because the hot room is exactly the condition that drives those compounds into the air you are breathing.
Cedar, hemlock, spruce and aspen
Western red cedar is the traditional premium choice: light, stable, naturally resistant to rot and insects, with the distinctive scent most people associate with a sauna. Hemlock is the common mid-range lining, close-grained and nearly odourless, which is the point for anyone sensitive to cedar's aroma. Nordic spruce, kiln dried and selected free of resinous knots, is the standard in Finland and is lighter in color. Aspen and alder are pale, odourless and very low in resin, which is why they often appear as bench material even in a cedar-lined cabin.
Lining versus benches versus the shell
A cabin usually uses more than one species for good reason. The shell and framing can be ordinary structural timber because it never gets hot on its face. The lining is where cedar, hemlock or spruce goes, since it is the surface radiating into the room. The benches take the most direct contact with skin, so low-conductivity, low-resin species such as aspen are preferred there even at a cost premium. When you compare two cabins on price, check which species is used where rather than reading the headline wood name alone.
Questions people ask about sauna wood
What is the best wood for a sauna?
Western red cedar for the traditional aroma and durability, hemlock if you want a near-odourless lining, Nordic spruce as the Finnish standard, and aspen or alder for benches because they stay cooler to touch.
Can I use pine in a sauna?
Knotty resinous pine should not line a hot room, because it weeps sap when hot. Kiln-dried, resin-free spruce and similarly selected softwood is a different matter and is used widely.
Should sauna wood be sealed or treated?
Interior sauna wood is left bare. Sealants and finishes are not rated for those temperatures and will off-gas or blister. Exterior cladding on an outdoor cabin is treated; the inside is not.