Sauna wood must be non-resinous softwood, low in thermal conductivity, dimensionally stable in heat and humidity, and completely unfinished. Western red cedar, Nordic spruce, hemlock and thermally modified aspen or alder are the four species that meet all four criteria. Everything else — hardwood, knotty pine, plywood, anything treated or sealed — fails on at least one, and usually in a way you discover by being burned or by smelling it.
This guide compares the working species for walls, ceilings and benches, sets out what must never be used, and explains the requirements behind the rules.
The four requirements
Every rule below follows from these.
1. Non-resinous. Resinous species — most pines, spruce with high pitch content, fir — weep sticky pitch at 190°F. It gets on skin and towels, it discolours, and it never really stops.
2. Low thermal conductivity. Dense woods conduct heat into your skin fast. A hardwood bench at 190°F can burn you on contact; a low-conductivity softwood at exactly the same temperature is comfortable. This is why the bench species matters more than the wall species.
3. Dimensionally stable. Sauna wood cycles from bone dry to humid and back, several times a week, for years. Species that move a lot will cup, twist and open at the joints.
4. Unfinished. No varnish, no stain, no paint, no standard wood oil. Every film-forming finish blisters, discolours and off-gasses at sauna temperatures, and you are breathing that air. Sauna wood is left bare, or treated only with paraffin-based sauna oil on bench tops.
A fifth, for outdoor exteriors only: rot and UV resistance.
The species compared
| Species | Thermal conductivity | Stability | Scent | Cost | Best for |
|---|---|---|---|---|---|
| Western red cedar | Low | Excellent | Strong, aromatic | High | Walls, ceiling, benches |
| Nordic spruce | Low | Very good | Faint, clean | Low–medium | Walls, ceiling |
| Hemlock | Low | Good | Almost none | Medium | Walls, ceiling |
| Thermo aspen | Very low | Excellent | None | Medium–high | Benches, backrests |
| Thermo spruce / alder | Low | Excellent | Faint | Medium–high | Walls, benches, exteriors |
| Basswood / linden | Very low | Good | None | Medium | Benches |
| Obeche | Very low | Good | None | Medium | Benches |
Western red cedar
The premium default, and the species most people picture.
Why it works: low thermal conductivity so it stays comfortable to touch; excellent dimensional stability; naturally rot- and insect-resistant, which matters in a humid environment; and the distinctive aroma that many people associate with sauna.
Grades:
- Clear — knot-free, uniform, the highest grade and the highest price
- Knotty (or "select tight knot") — visible knots, identical performance, substantially cheaper
Performance is the same. The premium is entirely visual. If the budget is tight, knotty cedar is where the money is.
Cost: $7–$12 per square foot knotty, $12–$20 clear.
The one real caveat: the scent is strong, particularly in the first months, and a minority of people find it overpowering or are sensitive to it. If anyone in the household is scent-sensitive, consider hemlock or spruce before committing.
Outdoors: cedar is excellent for exterior cladding, weathering to silver-grey if left untreated.
Nordic spruce
The traditional Finnish choice, and the value option.
Why it works: the species Finnish saunas have been built from for centuries. Pale, clean-looking, low thermal conductivity, good stability, and a faint fresh scent rather than a strong one. Nordic-grown spruce is tight-grained and low in resin compared with faster-grown species from warmer climates.
Cost: $4–$8 per square foot — the least expensive of the working species.
Where it goes: walls and ceilings, primarily. Usable for benches, though a low-conductivity species like thermo aspen is a noticeable upgrade for the surface you sit on.
A note on sourcing: "spruce" covers a range. Nordic or Baltic spruce sold specifically for sauna use is what you want; generic construction-grade spruce from a lumber yard is a different product with more knots and more resin.
Hemlock
The odourless option.
Why it works: light in colour, straight-grained, low conductivity, and — the point — almost no scent at all. For anyone who finds cedar overpowering, or who is sensitive to strong aromatics, hemlock is the answer.
Cost: $5–$9 per square foot.
Trade-offs: slightly less dimensionally stable than cedar or thermally modified wood, and no natural rot resistance, so it is an interior species only.
Common in: many pre-fabricated infrared cabins, where the low scent suits a cabin used for long sessions at lower temperatures.
Thermally modified woods
The best bench material available, and increasingly the default in high-end builds.
What thermal modification is: the timber is heated to 180–230°C in a controlled low-oxygen environment. This breaks down the hemicellulose and permanently changes the wood — it becomes dimensionally stable, resistant to rot and decay, darker in colour, and lower in thermal conductivity. It is a physical treatment, not a chemical one, so there is nothing to off-gas.
Thermo aspen is the standout for benches. Exceptionally low thermal conductivity, so it never gets uncomfortably hot to sit on even at 195°F; pale and fine-grained; completely odourless; dimensionally stable. $10–$18 per square foot.
Thermo spruce and thermo alder are used for walls, benches and exterior cladding. The dark brown tone is the basis of most contemporary sauna interiors, and the stability makes them excellent outdoors. $9–$16 per square foot.
Trade-offs: thermally modified wood is slightly more brittle than untreated timber, so it needs care during installation — pre-drill near ends. And the darker colour is a design decision, not a neutral one.
Make the bench tops thermo aspen. It is $300–$900 on a typical room and it is the surface your skin is in contact with for an hour a week.
Basswood, obeche and other bench species
Basswood (linden) — very low conductivity, no scent, pale and even. A good bench material and popular in some markets.
Obeche — a tropical hardwood with unusually low density and conductivity, traditionally used for sauna benches in Europe. Performs well; check the sourcing.
Abachi — another name for obeche in some markets.
These are legitimate bench choices where available. Thermo aspen has largely displaced them in North America on availability and price.
Woods that must never be used
| Wood | Why not |
|---|---|
| Any hardwood (oak, maple, ash, birch) | High density conducts heat into skin; burns on contact at 190°F |
| Knotty pine | Weeps pitch from the knots; sticky and permanent |
| Douglas fir, most softwood construction lumber | Resinous; pitch bleed |
| Plywood | Adhesives off-gas; delaminates in humidity |
| MDF, particle board, OSB | Swells, disintegrates, off-gasses |
| Pressure-treated timber | Chemical preservatives volatilise at heat. Never inside a sauna. |
| Any painted, stained or varnished wood | Blisters, discolours, off-gasses |
| Reclaimed timber of unknown history | May carry finishes, treatments or contaminants |
| Cypress, redwood | Sometimes suggested; resin and stability issues make them poor choices |
It is the most common serious error. A beautiful oak bench in a sauna is a burn hazard. Wood does not have a temperature problem; it has a conductivity problem. At the same 190°F, thermo aspen is comfortable and oak is not.
How each species ages
Worth knowing, because none of these woods stay the colour they arrive.
Western red cedar darkens and mellows over the first couple of years, moving from pinkish-brown toward a deeper, warmer tone. The aroma is strongest in the first few months and settles to a pleasant background presence. Outdoors and untreated, it silvers to a soft grey within one to three years.
Nordic spruce stays pale for a long time and yellows gradually. Bench areas darken faster than walls because of skin contact — which is the argument for towels and for annual sanding.
Hemlock ages similarly to spruce, going slightly golden. Because it starts almost white, staining shows more readily than on cedar, so bench discipline matters.
Thermally modified woods are the most colour-stable of the group, because the darkening happened in the kiln rather than being waiting to happen. They will lighten slightly with UV exposure outdoors but change very little indoors.
All of them develop dark patches on bench tops where bodies sit, from absorbed oils and sweat. This is normal, it is prevented by sitting on a towel, and it is removed by a light annual sand. A sauna where nobody uses a towel will need aggressive sanding within a few years and eventually new bench tops.
What accelerates ageing badly: a room that is never dried out after use, and a room run permanently at the top of the temperature range. Neither species choice nor finish compensates for either. → How to Clean and Maintain a Sauna
Choosing by element
Walls and ceiling. Any of cedar, Nordic spruce, hemlock or thermo spruce. The decision is aesthetic and budgetary — all four perform. Cedar for warmth and aroma, spruce for value and tradition, hemlock for no scent, thermo spruce for a dark contemporary tone.
Benches and backrests. Thermo aspen first, clear cedar second, basswood or obeche where available. This is the surface you touch; spend here.
Bench frames and supports. Same species as the tops, or a contrasting one used deliberately.
Door frame and trim. Match the walls, or use a single contrasting species across door trim, bench frames and vent surrounds to tie the room together.
Duckboard floor. Bench species, removable.
Exterior cladding, outdoor saunas. Thermally modified wood first, western red cedar second. Both weather to silver if left untreated.
Behind the cladding: framing lumber is ordinary construction timber — it is outside the vapour barrier and never sees sauna conditions. Battens between the vapour barrier and the cladding should be a non-resinous softwood.
Finishing and care
Walls and ceiling: nothing. Bare wood.
Bench tops: paraffin-based sauna oil, thinly applied once or twice a year after a light sand. This is the only finish that belongs in a sauna. It penetrates rather than films, and it tolerates the temperature.
Varnish, lacquer, polyurethane, stain, paint, linseed oil, teak oil or danish oil. All of them either blister, go tacky, or off-gas into the air you breathe.
Annual care: sand bench tops lightly with 120–180 grit to lift absorbed staining, vacuum, then re-oil if you use oil. Fifteen minutes.
Prevention beats treatment: always sit on a towel. Absorbed body oils are the main cause of the dark staining that makes old sauna benches look tired, and a towel prevents nearly all of it.
→ How to Clean and Maintain a Sauna
What it costs for a typical room
A 5' × 7' room with a 7-foot ceiling has roughly 240 square feet of wall and ceiling to clad, plus benches.
| Scheme | Cladding | Benches | Total materials |
|---|---|---|---|
| Nordic spruce throughout | $960 – $1,920 | $500 – $1,200 | $1,460 – $3,120 |
| Hemlock walls, aspen benches | $1,200 – $2,160 | $900 – $2,000 | $2,100 – $4,160 |
| Knotty cedar throughout | $1,680 – $2,880 | $1,000 – $2,200 | $2,680 – $5,080 |
| Clear cedar throughout | $2,880 – $4,800 | $1,400 – $2,800 | $4,280 – $7,600 |
| Thermo spruce walls, thermo aspen benches | $2,160 – $3,840 | $1,200 – $2,800 | $3,360 – $6,640 |
US market ranges, not store prices.
Nordic spruce or knotty cedar walls with thermo aspen bench tops. You spend where it matters and save where it does not.
→ How Much Does a Custom Home Sauna Cost?
Buying and installing sauna timber
Buy tongue-and-groove profiled for sauna use. Standard T&G panelling is often too thick, too wide or profiled for a different application. Sauna cladding is typically 12–15 mm thick and 90–120 mm wide — thin enough to come up to temperature quickly, narrow enough to move less.
Order 10–15% extra. Offcuts, defects and mistakes. Running short of a specific grade halfway through a wall is a genuinely annoying problem.
Acclimatise before installing. Bring the timber into the space for a few days so its moisture content settles. Wood installed straight off a cold truck will move afterwards.
Check the lengths will get into the room. Eight-foot boards and a basement stair with a turn is a combination worth measuring before ordering.
Fix with hidden nails through the tongue, or with clips. No face fixing on any surface skin touches.
Leave expansion gaps at floor and ceiling — typically 5–10 mm, covered by trim. Sauna timber moves, and boards fixed hard between two surfaces will cup or buckle.
Batten over the vapour barrier, typically 20 × 45 mm, running perpendicular to the cladding direction. This creates the air gap behind the boards that lets them dry from both faces.
Handle thermally modified wood carefully. It is more brittle than untreated timber; pre-drill near board ends.
Store spares. A few boards of each species kept somewhere dry will save you a colour-matching problem in five years.
Frequently Asked Questions
What is the best wood for a sauna?
Western red cedar for a warm, aromatic premium interior; Nordic spruce for the traditional Finnish look at the best price; hemlock where cedar's scent would be too strong; and thermally modified aspen for benches, because it has exceptionally low thermal conductivity and never becomes too hot to sit on. All four are non-resinous softwoods, which is the fundamental requirement.
Is cedar or hemlock better for a sauna?
Both perform well and the choice is mainly about scent. Cedar is aromatic, naturally rot-resistant and slightly more dimensionally stable, and it is the premium default. Hemlock is almost odourless, lighter in colour and less expensive, which makes it the right choice for anyone sensitive to cedar's strong aroma or who simply prefers a neutral room.
Can you use pine in a sauna?
Not knotty pine, which weeps sticky pitch from the knots at sauna temperatures and never stops. Some tight-grained, low-resin Nordic pine is used in Finland for walls, but it is not the same product as the construction-grade pine sold in most lumber yards. Nordic spruce is the safer and more widely available choice at a similar price.
What wood should you never use in a sauna?
Any hardwood such as oak, maple, ash or birch — dense woods conduct heat into skin and burn on contact at 190°F. Also knotty pine, Douglas fir and other resinous softwoods; plywood, MDF, particle board and OSB, which off-gas and disintegrate; pressure-treated timber, whose preservatives volatilise; and anything painted, stained, varnished or sealed.
Should you oil or seal sauna wood?
Walls and ceilings are left completely bare. Bench tops may be treated with a paraffin-based sauna oil made specifically for the purpose, applied thinly once or twice a year after a light sand. Never use varnish, lacquer, polyurethane, stain, paint or standard wood oils such as linseed, teak or danish — they blister, go tacky and off-gas into the air you breathe.
See the woods in finished saunas
Cedar, pine and spruce barrels, cabins and indoor rooms — browse the range to see how each species looks built.
Barrel Saunas Indoor SaunasRelated guides
- How to Design a Custom Sauna
- Custom Indoor Sauna Design Ideas
- How to Clean and Maintain a Sauna
- Custom Home Sauna: Complete Buying Guide
- Outdoor Sauna Buying Guide
Published by Finest Saunas