Sauna timbers compared: western red cedar, hemlock, aspen and more

Before you compare species

Two ideas explain most of the differences between sauna timbers. Both are covered in our guide to choosing sauna timber, so here is the short version:

• Lower density means a gentler feel on the skin. Every surface heats towards the air temperature, but light, dry timber passes that heat to your skin slowly.
• Benches and walls do different jobs. Anything you touch should be clear (knot-free) and resin-free. Walls and ceilings can be chosen more for appearance and scent.

The species notes below build on those principles. Density figures are typical air-dry values from wood-science references; individual boards vary.

The timbers we use

Western red cedar is our principal sauna timber. We use it for most of the saunas we design and build, for walls, ceilings and, in clear grades, benches and backrests. It is light, stable, comfortable to touch and naturally durable, and Australian timber references rate its heartwood as termite-resistant, which counts in Queensland. We sometimes use Canadian hemlock, usually where a client wants a paler, calmer interior with almost no scent.

The other species in this guide are legitimate sauna timbers used by respected manufacturers around the world. We describe them so you can compare options and understand what you see elsewhere, not because we routinely build with them. If one of them suits your project, talk to us about it.

Western red cedar: our principal timber

• Origin: Thuja plicata, from western North America. Not a true cedar, and not the same as Australian red cedar.
• Appearance: heartwood from pinkish-brown to deep chocolate, often with streaks; pale sapwood. Straight grain, coarse texture.
• Aroma: strong, sweet and long-lasting.
• Resin: not a resinous timber. Its colour and durability come from water-soluble extractives.
• Heat feel: among the lightest common sauna timbers, at roughly 340–380 kg/m³ depending on the reference.
• Stability: the lowest shrinkage of the mainstream sauna species, and it resists warping and checking well.
• Splinters and wear: soft, so it dents and scratches easily. Edges can lift where the grain runs out, so rounded edges help.
• Ageing: darkens gradually indoors, faster where steam hits; greys outdoors.
• Maintenance: extractives can leave tan marks when wet, and iron fixings stain it blue-black, so only stainless or other non-staining fixings should be used.
• Durability: naturally durable heartwood. WoodSolutions and the Queensland Government rate the heartwood termite-resistant, which matters in Queensland, especially for outdoor saunas.
• Best for: walls, ceilings and, in clear grade, benches; outdoor sauna cladding.
• Less suited to: knotty boards on seats; people who dislike a strong scent; very heavy commercial wear without replaceable slats.

Why it is our first choice: it combines low density (comfortable to sit against), the lowest movement of the mainstream species (boards stay flat and tight through years of heating and cooling), natural durability and a warm, varied colour that looks finished without any coating. The trade-offs to accept: a strong scent, a soft surface that marks under heavy use, and colour that varies from board to board. Clear grades also cost more than knotty ones.

Clear or knotty western red cedar

Western red cedar is sold in appearance grades. The cedar industry’s siding grades include Clear Heart (heartwood on the exposed face), A Clear (slightly more natural characteristics) and knotty grades such as Select Knotty, with sound, tight knots. Grade names vary between product lines, so specify the grade and the grading rules on every order.

• Clear gives a calm, contemporary interior and is the grade for benches, backrests and headrests.
• Knotty suits walls and ceilings where you want a more rustic look or need to manage the budget.

Eastern white cedar

• Origin: Thuja occidentalis, from north-eastern North America. Also called northern white cedar.
• Appearance: light reddish-brown heartwood with nearly white sapwood. Small pin knots are common.
• Aroma: a cedar scent that is milder than western red cedar’s.
• Resin: not described as resinous.
• Heat feel: very light, at around 350 kg/m³, similar to western red cedar.
• Stability: low shrinkage, close to western red cedar.
• Splinters and wear: soft and weak, with poor screw-holding, so fixings and bench supports need care.
• Ageing: weathers to grey outdoors.
• Durability: rated durable to very durable against decay, which suits outdoor saunas.
• Best for: outdoor sauna bodies and interiors where a paler cedar and gentler scent are wanted.
• Less suited to: where a fully knot-free look is essential, unless a clear grade is available.

Aspen and thermally modified aspen

• Origin: European aspen (Populus tremula) is the usual sauna aspen; quaking aspen (P. tremuloides) is the North American species. A botanical hardwood.
• Appearance: natural aspen is pale yellow to almost white with a straight grain and even texture. Thermo aspen is golden to mid-brown.
• Aroma: none to speak of. Thermo aspen has a mild smoky scent.
• Resin: effectively none in either form.
• Heat feel: light, at roughly 415–450 kg/m³ for natural aspen. Thermal modification lowers heat transfer further: the ThermoWood handbook reports 20–25% lower conductivity than untreated softwood.
• Stability: natural aspen moves moderately and can warp if poorly dried, so kiln quality matters. Thermo aspen is much more stable.
• Splinters and wear: well-machined and sanded aspen is smooth, but blunt tooling can leave a fuzzy surface. Thermo aspen is more brittle at edges and ends.
• Ageing: natural aspen shows sweat and water marks and darkens with use. Thermo aspen’s darker colour hides marks better.
• Maintenance: towels, regular cleaning and light sanding. Sauna paraffin oil can help resist staining. Seal the end grain of thermo aspen bench boards.
• Best for: benches, backrests and headrests in both forms; walls where a pale or mid-brown interior is wanted.
• Less suited to: structural bench frames; pale natural aspen in busy rooms without a strict towel and cleaning routine.

Alder and thermally modified alder

• Origin: black or common alder (Alnus glutinosa) from Europe, or red alder (A. rubra) from North America. A botanical hardwood, despite sometimes being sold as a softwood.
• Appearance: light tan to reddish-brown with a fine, even grain. Thermo alder is hazel to deep brown.
• Aroma: none characteristic; thermo alder has the typical smoky note.
• Resin: resin-free in practice.
• Heat feel: a little denser than aspen, at roughly 380–600 kg/m³ for black alder, typically around 490.
• Stability: moderate when natural; much better when thermally modified.
• Splinters and wear: fine, uniform texture that finishes smoothly. Thermo alder shares the brittleness of all thermo timber.
• Ageing: darkens and reddens over time.
• Maintenance: responds well to sauna paraffin oil, which deepens its colour.
• Best for: benches and walls, especially where a warmer tone is wanted. Thermo alder suits busy rooms.
• Less suited to: structural framing; anyone wanting a very pale, unchanging interior.

Nordic spruce

• Origin: Norway spruce (Picea abies), traded as European or Nordic whitewood.
• Appearance: creamy white with a fine, straight grain. Usually knotty.
• Aroma: little or none once dry.
• Resin: some, though considerably less than pine. Resin can bleed at knots when heated. Thermo spruce is resin-free.
• Heat feel: light, at around 405 kg/m³.
• Stability: moderate.
• Ageing: darkens with use, like all sauna timber.
• Best for: walls and ceilings, where it is the traditional Finnish lining; bench frames, where its resin is hidden.
• Less suited to: seats and backrests, and knotty boards directly above the heater.

Canadian hemlock

This is the timber we use when a client wants something paler and quieter than cedar.

• Origin: western hemlock (Tsuga heterophylla) from coastal British Columbia and the Pacific Northwest. “Canadian hemlock” is sold under both this name and T. canadensis, so ask for the botanical name.
• Appearance: pale brown, sometimes with a purplish tinge; straight grain with a coarser, less even texture than cedar.
• Aroma: none characteristic, which makes it a good neutral choice.
• Resin: non-resinous.
• Heat feel: denser than cedar and at the upper end of aspen’s range or above it, at roughly 430–505 kg/m³ (WoodSolutions, the Australian timber industry reference, gives 505 kg/m³ seasoned).
• Termites: rated not termite-resistant by WoodSolutions, with durability Class 4 (the lowest) above and in ground.
• Stability: shrinks noticeably more than cedar with changes in moisture (12.4% volumetric shrinkage in US Forest Products Laboratory figures, against 6.8% for cedar). Claims that it “doesn’t warp” depend on good drying and grade.
• Knots: sauna hemlock is normally sold clear, but knot-free is a grade, not a property of the species.
• Best for: walls and ceilings, particularly for people who prefer no scent.
• Less suited to: benches where a lighter species is available, although clear hemlock benches are used by some manufacturers.

Abachi (ayous)

• Origin: Triplochiton scleroxylon from West and Central Africa. Also traded as obeche, ayous, samba and wawa.
• Appearance: pale yellow to creamy white, near knot-free. Interlocked grain can tear out when machined.
• Aroma: unpleasant when green, but largely gone once dry.
• Resin: none reported.
• Heat feel: very light, at around 380 kg/m³, making it one of the coolest bench timbers. Klafs, the German sauna maker, fits obeche (abachi) headrests and backrests as standard in its Premium sauna.
• Stability: low shrinkage.
• Durability: not durable, with poor resistance to decay and termites; suited to dry interior use.
• Best for: benches, backrests and headrests.
• Less suited to: projects where certified supply cannot be confirmed. Australian availability should be checked early.

Its dust, like cedar’s, is a known sensitiser for the people who machine it. That is a workshop issue requiring dust control, not a risk to bathers.

Poplar and “magnolia”

True poplars (Populus species) are light to medium-density hardwoods, and some sauna suppliers offer pale, knot-free, resin-free poplar for benches and interiors. “Magnolia” sauna boards are usually Liriodendron tulipifera, known as yellow-poplar or tulipwood. Despite the name, it is not a true poplar. It is offered in thermally modified form for benches and interiors. Neither is widely documented for sauna use, and Australian supply should be confirmed before specifying.

Basswood (linden)

“Linden” covers two different timbers. American basswood (Tilia americana) is pale, soft and light, at around 415 kg/m³, but it has the highest shrinkage of the species in this guide, a concern in a room that heats and dries repeatedly. European lime (Tilia × europaea), the “linden” usually sold by European sauna suppliers, is denser, averaging about 535 kg/m³, so it is not one of the coolest bench timbers, although it moves less than basswood. Its use for benches comes from Eastern European tradition rather than heater or sauna manufacturers’ documentation. Ask which species is being offered, and treat either as a specialty choice rather than a default.

Comparison table

Movement is ranked from published shrinkage figures and is relative. Real-world movement in a well-dried, well-ventilated room is a fraction of these laboratory values.

Strengths and trade-offs at a glance

No timber is best at everything. This is the honest summary of what each one gives you and what it costs you.

Aromatic or low-aroma?

Scent is a matter of taste, and it is worth deciding early. Western red cedar has the strongest, longest-lasting aroma, which many people associate with a real sauna and some find overwhelming. Eastern white cedar is milder. Hemlock, aspen, alder and abachi are close to scent-free, which suits people who prefer a neutral room or who are sensitive to strong smells. Thermally modified timbers carry a faint smoky note that fades over time; some makers say it never disappears entirely. If you are unsure, smell an offcut before you commit to a whole room.

How sauna timber ages

Every sauna timber changes colour, and a well-used room should look lived-in rather than new.

• Indoors, timber darkens gradually with heat and light. Areas near the heater and where water lands darken fastest.
• Benches mark first. Sweat, skin oils and water leave darker patches where people sit and lean, which is why towels are recommended and why lighter timbers show wear sooner.
• Western red cedar deepens towards honey and brown tones and keeps its character well.
• Pale timbers such as aspen and hemlock show use more readily; thermally modified timbers hide it better because they start darker.
• Outdoors, unprotected timber turns silver-grey, faster in strong sun. A sauna-appropriate exterior finish slows this; the interior stays unfinished.

Light sanding along the grain refreshes worn benches. Our care guide covers cleaning, bench oil and what not to use.

Common myths

• “Cedar doesn’t absorb heat.” Every surface in the room approaches air temperature. Low-density timber simply passes heat to your skin more slowly.
• “Thermally modified timber is stronger.” It is more stable, but splitting and bending strength fall. Benches need adequate thickness, support and sealed ends.
• “The smell of thermo timber goes away.” It fades. The ThermoWood handbook says it becomes hard to notice except close up, while some makers say it never disappears entirely.
• “Hemlock never warps.” It moves more than cedar; performance depends on drying and grade.
• “Magnolia is a kind of poplar.” Magnolia sauna boards are usually yellow-poplar, which is not a true poplar.
• “Alder is a softwood.” It is a botanical hardwood.
• “Cedar dust makes cedar saunas unhealthy.” The evidence concerns people sawing and sanding the timber, not people using a finished sauna.
• “Australian hardwood is better inside the hot room.” Dense eucalypts such as spotted gum and jarrah pass heat to skin much faster. They belong outside the hot room.
• Unquantified claims such as “repels insects”, “low flammability”, “never splinters” or “purifies the air” are marketing, not established properties.

Termites and Queensland

Termites are a real consideration for outdoor saunas and for any timber in contact with the building structure in Queensland, where both subterranean and drywood termites occur. Australian timber references rate western red cedar heartwood as termite-resistant. Western hemlock and radiata pine are rated not resistant. Thermally modified timber is not termite-resistant: the ThermoWood Handbook and the Lunawood manufacturer both say so, whatever its other improvements. We found no Australian termite rating for aspen, alder, spruce or abachi, all of which are non-durable timbers; The Wood Database describes abachi as having poor resistance to termites.

Inside a sauna, the timber that matters most for termites is usually not the lining but the structure behind it and, for outdoor saunas, the base and subfloor. Termite management for those is part of the building design and a matter for the builder and certifier. Do not use preservative-treated timber for benches or hot-room linings unless the timber, heater and treatment manufacturers all confirm it is suitable at sauna temperatures.

For bench detailing, thermal modification and finishes, see Choosing sauna timber. If you are choosing a kit rather than a custom room, Outdoor sauna kits in Queensland covers the cedars used in our kit range.