Best Wood for a Sauna: How Cedar, Basswood, Spruce, Aspen and Thermo-Wood Compare

Sauna wood guide

There is no single best wood for a sauna. The right choice depends on the heat (infrared or traditional), whether the sauna stands indoors or outdoors, how much scent you want and your budget. What separates sauna woods is stability through heat and moisture, how hot the surface feels, resin and knots, scent and, outdoors, decay resistance. This guide compares our brands' woods using USDA data and manufacturer care rules.

Every example is a model Sauna Republic carries; most physical data come from the USDA Forest Products Laboratory's Wood Handbook.

What a sauna wood has to do

Five properties decide where each wood fits.

Stability through heat and moisture

Wood swells as it absorbs moisture and shrinks as it dries. Dundalk LeisureCraft's Harmony barrel manual notes that, with local humidity and weather, "the cedar will either shrink or expand," and SaunaLife's GL4 manual calls some cracking or warping normal given a sauna's "extreme temperature and humidity fluctuations." The handbook's shrinkage figures, in the table below, are laboratory values, not a measure of how much a finished wall moves.

How hot the surface feels

Wood conducts heat slowly. The Wood Handbook puts structural softwood lumber at 12% moisture content at 0.10 to 0.14 watts per meter-kelvin (W/m-K), against 45 for steel, and explains that wood "does not feel extremely hot or cold to the touch as do some other materials." Conductivity rises with density and moisture content. The cedars and basswood sit at the low end of its species table, but the handbook warns that values "may vary by as much as 20%," and we found no test comparing how benches of different species feel.

Resin and knots

The handbook's chapter on wood structure lists pine and spruce among the softwoods with resin canals and says such canals are absent in the normal wood of other softwoods, a group that includes the cedars and hemlocks. Its finishing chapter adds that "Many pines contain pitch" and that knots of almost all species carry oils and resins. Some makers specify knot-free boards: SaunaLife lists knot-free thermo-aspen benches, and Clearlight specifies "grade 'A' clear" mahogany. The canal statement covers softwoods only; it does not make aspen, alder or basswood resin-free.

Scent

Western red cedar has a characteristic smell; the handbook describes dry basswood as "without odor or taste." See scent and allergies below.

Decay resistance, mainly outdoors

Heartwood decay ratings, summarized in the table, matter most outdoors, and the handbook adds that "Untreated sapwood of essentially all species has low resistance to decay." Inside a hot room, the Finnish Sauna Society and the brands focus on cleaning, drying and ventilation instead.

Sauna wood types, species by species

What wood is used for saunas? Here is the evidence on each wood our brands use, with details from our listings and, where checked, the manufacturers' pages.

Basswood

North American basswood is one of Clearlight's two cabin woods, and a light one: Purdue Extension puts it at about 26 pounds per cubic foot at 12% moisture content. The handbook's species chapter rates its drying shrinkage "as high; however, basswood seldom warps in use." On scent, the handbook says "When dry, the wood is without odor or taste," while Purdue notes "a faint musty odor, especially when wetted," so the fair summary is little or no scent when dry. Clearlight calls basswood "hypoallergenic, odor-free"; we found no independent test of any finished sauna wood for allergy, so read that as Clearlight's description.

Mahogany

Clearlight says it builds its Premier and Sanctuary models from "eco-certified, grade 'A' clear mahogany or North American basswood," chosen as one wood type per cabin, and its Sanctuary Outdoor models have mahogany interiors. Clearlight does not name the mahogany species, so we cannot match it to handbook data. See the Clearlight indoor collection, our Clearlight saunas buying guide and the Sanctuary vs Premier guide.

Western red cedar

The handbook describes western red cedar heartwood as "reddish or pinkish brown to dull brown." It owes its decay resistance to extractives, natural chemicals in the heartwood, though their roles are not fully understood: a 2012 field study linked plicatic acid to decay resistance in ground contact and found the long-credited thujaplicins "only weakly associated." Its smell comes mainly from methyl thujate, according to a 1958 Forest Products Journal paper.

Finnmark lines the FD-4 Trinity and FD-5 Trinity XL hybrids with western red cedar, per our listings. Clearlight's current saunas are not cedar; in its range, cedar appears on the Clearlight Plunge's cabinet, which our listing describes as Canadian cedar.

Eastern white cedar

Eastern white cedar is the handbook's northern white-cedar: "lightweight, rather soft, low in strength and shock resistance, and with low shrinkage upon drying." The handbook does not describe its scent.

Dundalk LeisureCraft builds every outdoor Canadian Timber sauna we carry from it, including the CT Barrel and the CT Elation, a barrel with a flat floor and cedar bevel siding. Stave and plank walls mean the same cedar forms both faces. Mind the name: Dundalk also lists a separate red cedar Luna, but the Canadian Timber CT Luna we carry is eastern white cedar, per Dundalk. Compare models in our Dundalk LeisureCraft buying guide.

Hemlock

In our range, hemlock appears as the entry ramp of the wheelchair-accessible Clearlight Sanctuary Retreat, per our listing; no sauna we carry lists it for walls or benches.

Nordic spruce, aspen and alder

SaunaLife's G2 pairs Nordic spruce wall beams with knot-free aspen benches. Iglucraft lines its Iglusaunas with aspen under spruce shingles. Auroom offers aspen or thermally modified aspen on its indoor kits, alder as an option on some, and waxed dark-gray alder walls in its Terra cabins. Harvia's design guide offers "reddish brown alder, light-coloured aspen or dark, heat-treated aspen" for benches.

The handbook has no entry for Norway spruce, the species sold as Nordic spruce, and its aspen and alder data describe North American species. Neither Harvia nor any other source we could verify explains why aspen and alder are favored for benches.

Thermally modified wood

Thermally modified wood (thermo-spruce, thermo-pine, thermo-aspen, thermo-alder) is timber heated until its properties change. A 2009 review in BioResources describes industrial processes at 320 to 500 °F (160 to 260 °C), and a 2021 review in the Journal of Materials Science puts commercial production usually at 320 to 464 °F (160 to 240 °C). The handbook's specialty treatments chapter says heating "can decrease the hygroscopicity and improve the dimensional stability and decay resistance" of wood, "requiring no added chemicals." Both reviews note that treated wood comes out darker.

The trade-off is strength. The handbook says the gain in stability and durability "also increases the brittleness and loss in some strength properties," and one study cited in the 2009 review found bending strength fell by about half for spruce treated at 428 °F (220 °C). Decay resistance improved in laboratory tests, but heat-treated wood "is not recommended to be used in ground contact."

A thermally modified wood sauna is common in our range: SaunaLife's thermo-spruce barrels and cabins, Auroom's outdoor cabins and thermo-aspen kit options, the thermo-alder interior of the Haljas Houses Hele Nano, ThermaSol's thermally modified aspen benches in nine of the eleven cabins we list, and Dundalk's indoor CT Element. Our SaunaLife, Auroom and ThermaSol buying guides cover the models.

Sauna wood comparison at a glance

Handbook data are for North American species: heartwood decay group, conductivity in W/m-K at 12% moisture content, and volumetric shrinkage from the green (undried) dimension.

Infrared vs traditional: what changes for the wood

A traditional sauna heats air and stones, and water on the stones adds humidity. A Cleveland Clinic overview describes traditional saunas as "typically heated between 150 degrees Fahrenheit and 195 F" (about 66 to 91 °C) and notes that "temperatures in infrared saunas typically land between 110 F and 135 F" (about 43 to 57 °C). Clearlight's infrared sauna FAQ says "Only about 20% of the heat from our heaters goes to heat the air."

For the wood in an infrared cabin, that means cooler air and no water, so apart from sweat it stays dry, the condition in which the handbook describes basswood as without odor. The heaters still sit in the walls, so the wood around them warms, and a small closed cabin makes scent part of every session. What does not change: the heat cycles, knots where skin touches, and the manufacturer's finish rules. Hybrids such as the FD-4 Trinity, which adds a Harvia heater and stones to its infrared heaters, face both. Our Finnish sauna vs infrared sauna comparison covers the rest.

Indoor vs outdoor sauna wood

Outdoors, wood also faces sun, rain, snow and the ground, so decay resistance matters. Cedar heartwood is rated "Resistant." Thermally modified wood resisted decay better than untreated wood in laboratory tests, but neither the handbook nor the 2009 review supports soil contact. Whatever the species, keep it off wet ground: Dundalk's Serenity barrel manual asks for a level base "with a slight slope to the back for drainage," and SaunaLife's GL4 manual calls for replacing the soil beneath "with a well-drained and load bearing material."

Unfinished wood also weathers. The handbook's finishing chapter says extractives change color under UV and visible light and that, in advanced weathering, "wood may develop a bright silvery-gray sheen." A 2007 laboratory study notes that weathered western red cedar surfaces are "susceptible to black stain caused by fungi."

Exterior care, brand by brand

Compare models in our best outdoor saunas guide.

Sauna wood finishes and care

Inside the hot room, the brands whose guidance we checked agree: leave the wood bare or use only a product made for saunas.

Darkening is normal. Harvia's support article says "It is perfectly normal for the wooden surfaces of the sauna to darken over time," and that protective agents on the walls, which it says have poor heat resistance, can speed it up.

Hygiene comes from routine, not species

Cedar is sometimes sold as naturally antibacterial. The research we found ties cedar's extractives to the wood's own decay resistance, not to cleaner benches, and the 2007 study found that one staining fungus tolerated the cedar compound β-thujaplicin. The Finnish Sauna Society's hygiene guidance names no wood. It says bacteria on benches "mostly match the flora found on the skin," and that the amount of fungi and mould "depends on the humidity." Its advice: "Clean the sauna immediately after use," never use a high-pressure washer, and dry the room with the heater's remaining heat "aided by intensified ventilation." Harvia's maintenance article says to "Keep the heater on for approximately 10 minutes to dry the wooden parts." Between cleanings, a towel between you and the bench keeps sweat off the boards.

Scent, allergies and cedar

Clearlight says "Cedar has a subtle, aromatic scent that can be overwhelming for people with multiple chemical sensitivities."

The health evidence on cedar concerns dust, not saunas. CCOHS, Canada's occupational health agency, says in its fact sheet on workplace wood dust that "Western red cedar is a wood that has a clear association with the development of asthma," and a 1988 review indexed by NIOSH identified plicatic acid as the causative agent. Occupational asthma has also been reported with eastern white cedar dust, according to a NIOSH-funded surveillance newsletter citing a 1994 study.

How to choose the best wood for a sauna

Start from heat type and location; scent and budget narrow it from there.

Frequently asked questions

Browse indoor saunas and outdoor saunas to compare woods model by model.

Clearlight, Premier and Sanctuary are trademarks of Sauna Works, Inc., dba Clearlight Infrared. Sauna Republic is an authorized Clearlight dealer. Dundalk LeisureCraft, SaunaLife, Auroom, Iglucraft, Haljas Houses, ThermaSol, Finnmark, Harvia and HUUM are trademarks of their respective owners. Installation and electrical requirements vary by model and location; follow the manufacturer's manual and use a licensed electrician where required.