Common choices
| Wood | Best for | Notes |
|---|---|---|
| Nordic spruce | walls, ceiling | The Finnish classic; inexpensive, light; knots can get hot and release resin, so choose clear grades near the heater |
| Aspen | walls, benches | Low resin, pale, smooth, stays cool to touch; popular for benches |
| Alder | benches, walls | Low resin, warm reddish tone |
| Western red cedar | walls, barrels, benches | Aromatic, very stable and rot-resistant; the scent and dust bother some people |
| Hemlock | walls, benches | Light, no strong smell, little resin; common in North American kits |
| Thermally modified wood (thermo-aspen, thermo-pine, thermo-spruce) | walls, barrels, benches | Heat-treated: darker, more stable, less resin; often used for outdoor barrels and cubes |
| Abachi | benches | Very low heat conduction, stays cool, pale |
Thickness
- Panelling: 12–15 mm.
- Benches: 28–42 mm slats with gaps.
- Barrels: staves typically 40–45 mm.
- Log saunas: 70–120 mm logs or more.
Never use
Pressure-treated, painted or varnished wood inside the hot room, or particle boards and plywood with glues not rated for the heat. Interior surfaces stay bare or get a sauna-specific wax or oil only where the maker allows.