Sauna Wood Types: Cedar vs Hemlock vs Basswood vs Thermally Modified, and Does It Matter

Type "best wood for sauna" into Google and you get ten near-identical articles. Cedar builders rank cedar first. The company that sells thermally modified wood ranks that first. A wellness blog with an affiliate link to a basswood bench kit ranks basswood first. None of them tell you who is paying their bills.

Here is the actual answer: the wood species matters a lot in one situation and barely at all in another.

The 30-Second Answer

If you are still deciding between a kit, a DIY build, or a pre-built unit, read DIY vs kit vs pre-built first. Wood species is one line item inside that bigger decision.

Why Every Search Result Agrees With Itself

Run the search yourself. Sun Valley Saunas, Nordica Sauna, Tahoe Sauna Company, and half a dozen similar sites sell cedar barrel and cabin kits, and their "best wood" articles rank cedar first. Thermory sells thermally modified wood and its own guide ranks thermal modification as the premium choice. Plunge sells its own kit line and frames the comparison around what Plunge ships.

That is not a conspiracy. It is just normal content marketing, and it means almost nobody has published an answer to "does this actually matter" that isn't also a sales pitch for the answer they gave. We do not sell wood, kits, or saunas, so we have no reason to prefer any of these answers over the others. Here is what independently verifiable sources actually say.

What the Wood Science Actually Says

The most-cited technical claim in every one of these articles is some version of "cedar resists rot naturally." That one holds up. The USDA Forest Products Laboratory's Wood Handbook, the standard US reference on wood as a building material, classifies western redcedar as resistant or very resistant to decay, based on natural extractive compounds (thujaplicins) in the heartwood that are toxic to decay fungi. Hemlock, aspen, and basswood, the three next-most-common sauna woods, are all classified as slightly resistant or nonresistant in the same reference.

That single fact is doing most of the real work in "which wood should I buy." It is also the one claim that is genuinely load-bearing for an outdoor structure and much less relevant for an indoor room that never sees rain.

Dundalk LeisureCraft, which sells both cedar and hemlock/thermowood builds, says as much in its own comparison guide: hemlock, and untreated pine or spruce, are "not naturally rot-resistant" and the company does not recommend them outdoors without treatment. That is a manufacturer stating a limitation of a cheaper product it also sells, which is a stronger signal than a ranked listicle with no skin in the game either way.

Thermally Modified Wood: The Real Alternative to Cedar

Thermally modified wood (sometimes sold as "Thermowood," a brand name used by several suppliers) is spruce, pine, aspen, or a few other species heated in a low-oxygen kiln to roughly 356 to 482°F. The heat breaks down hemicellulose, the wood sugars that fungi and insects feed on, and drives out moisture. The result resists rot and mold without chemical treatment and holds up better than the same untreated species through repeated heat and moisture cycling.

It is not a free upgrade. LeisureCraft's own published comparison of cedar, hemlock, and thermowood states that thermal modification "reduces strength, with bending strength dropping by up to about a third" compared to the untreated wood. That is the manufacturer's own tradeoff disclosure, not a competitor's attack, and it is worth asking about if the wood is doing any structural work rather than just paneling.

Thermally modified wood also costs more than the untreated species it started as, which is why it shows up mostly in premium indoor builds rather than as the budget option.

Why Finnish and North American Brands Disagree About Cedar

Here is something none of the ranked listicles mention: the brands most associated with authentic Finnish sauna culture barely use cedar at all.

Harvia's own official guidance for choosing sauna bench wood ranks species by moisture handling in this order: spruce, then pine, alder, aspen, and heat-treated alder. Cedar is not on the list. Harvia explains that it prioritizes low-density, porous wood for benches specifically because "they don't heat up too much and are comfortable to sit or lean on," and recommends spruce for its natural resin content in colder, outdoor-adjacent use. This is a Finnish-heritage manufacturer's actual species lineup, not a marketing ranking.

Compare that to Almost Heaven Saunas, a US barrel and cabin builder whose product catalog lists 15 cedar products against 2 Nordic spruce products, and whose standard lumber samples are "Rustic Fir" and "Rustic Red Cedar." Dundalk LeisureCraft runs two full product lines split by cedar grade: the Canadian Timber line in Eastern White Cedar at a lower price point, and the Dundalk Collection in Western Red Cedar (knotty or clear grade) at a premium, described by the company as having "a richer colour, warmer aroma, and slightly higher natural oil content."

Neither camp is wrong. North American barrel and cabin brands build backyard structures that sit outside through winter, so cedar's weather resistance is a real functional requirement and the brands built their whole identity around a locally abundant wood that happens to solve that problem. Nordic-heritage brands build primarily for indoor installation inside an already-weatherproof building, where rot resistance is not the binding constraint, so the traditional species lineup optimizes for bench comfort and moisture handling in a sauna room instead. If you are comparing Almost Heaven against Dundalk or looking at Harvia against Huum, the wood each brand defaults to is a clue about what problem it was originally built to solve, not a universal ranking.

The Aroma and Sensitivity Question

Cedar's smell is real, strong, and polarizing. It is also worth being precise about the actual health question buried inside "is cedar bad for me."

Western red cedar wood dust is a well-documented cause of occupational asthma, driven by a compound called plicatic acid in the wood. This is established, peer-reviewed occupational medicine, going back decades, and it is the most common form of occupational asthma in parts of the Pacific Northwest lumber industry. But that research is about sustained exposure to airborne sawdust in mills and workshops, not about sitting in a finished, sealed cedar-paneled room. Nobody has published a study measuring whether heated, finished cedar paneling in a sauna produces comparable airborne exposure, so we are not going to tell you it does.

What we can tell you: if you dislike the smell, or you know you are sensitive to strong wood aromas for any reason, hemlock and most thermally modified species are close to odorless at sauna operating temperatures. That is a real, easy fix that does not require resolving an open science question.

Bench Wood Is Its Own Decision

Whatever the walls are made of, the bench and backrest are the wood you are actually touching at the hottest point in the room. This is where density matters more than species tradition. Lower-density wood conducts less heat into your skin, which is why basswood, aspen, and alder show up constantly as bench and backrest material even inside cedar-walled saunas, and why Harvia's own bench guidance leads with the same low-density, porous-wood logic. If you are configuring a kit that lets you mix a wall species with a separate bench species, that upgrade is worth the small cost more consistently than a wall-species upgrade is.

What to Actually Do With This

1. Outdoor barrel or cabin: budget for real cedar, or a genuinely thermally modified wood if you want the look without the cedar price or aroma. Do not accept untreated hemlock, spruce, or pine outdoors without a real maintenance plan; see our barrel sauna insulation guide for how the wall assembly and moisture management fit together.
2. Indoor sauna: treat wood species as an aesthetic and comfort choice, not a durability requirement. Spend the savings on electrical or ventilation instead, where the money changes something structural.
3. Any install: ask specifically about bench wood, separate from wall wood, and lean toward the lower-density option there regardless of what you pick for the walls.
4. Sensitive to aroma: ask for hemlock or thermally modified paneling instead of cedar. It is a simple substitution, not a downgrade.
5. Comparing kits: if a seller's "premium wood upgrade" doesn't tell you which of these actual tradeoffs it buys you, ask. A vague upsell is a marketing decision, not a wood-science one. Our sauna buying regrets roundup has more on how cheap, untreated materials show up as real problems within a season.

FAQ

What wood type should I look for and does it actually matter?

It depends on where the sauna goes. For an outdoor barrel or cabin sauna exposed to weather, wood species matters functionally: western red cedar has documented natural decay resistance that cheaper species lack, so it is worth the premium or the equivalent premium for a genuinely thermally modified alternative. For an indoor sauna protected from rain and snow, species is mostly an aroma and comfort choice, and paying a large premium for cedar there is optional, not structural.

Is cedar actually better than hemlock, or is that just marketing?

For outdoor durability, yes, and this is one of the few claims in this space with a real primary source behind it: the USDA Forest Products Laboratory classifies western redcedar as resistant to decay and hemlock as nonresistant. For an indoor sauna, the practical difference shrinks to aroma, cost, and how the wood looks, where hemlock is a legitimate lower-cost, low-aroma option rather than a compromise.

Is thermally modified wood as good as cedar?

It solves the same rot-resistance problem through a different mechanism (heat treatment instead of natural oils) and holds up well through repeated heat and moisture cycling. The tradeoff, according to LeisureCraft's own comparison of the two, is reduced bending strength after modification and a higher price than the untreated wood it started as. It is a legitimate alternative to cedar, not strictly a better or worse one.

Is cedar bad for allergies or breathing problems?

Western red cedar dust is a documented cause of occupational asthma in people with sustained exposure to airborne sawdust, such as mill and woodworking employees. That research does not extend to sitting in a finished, sealed cedar sauna, which has not been separately studied for airborne exposure. If you are sensitive to strong wood aromas for any reason, hemlock and most thermally modified species are a simple, close-to-odorless substitute.

Why do European sauna brands rarely use cedar?

Finnish and Nordic-heritage brands like Harvia build primarily for indoor installation, where rot resistance from weather exposure is not the deciding factor, so their traditional species lineup (spruce, pine, alder, aspen) optimizes for bench comfort and moisture handling in an already-weatherproof room. North American barrel and cabin brands build backyard structures that sit outside year-round, where cedar's natural weather resistance is a real requirement, which is why cedar became the default there instead.

Sources

• USDA Forest Products Laboratory: Wood Handbook, decay resistance classification
• Mechanism of occupational asthma due to western red cedar (Thuja plicata), PubMed
• Wood Dust and Asthma, PMC
• Harvia: Choosing sauna benches, frequently asked questions
• LeisureCraft: Cedar vs Hemlock vs Thermowood sauna wood guide
• Almost Heaven Saunas: lumber samples
• Almost Heaven Saunas: barrel sauna collection