Sign in

Products · Building a sauna · Thermory

Thermory Thermo-Aspen Sauna Bench Boards, profile SHP (thermally modified aspen)

Reader ratings
Thermory Thermo-Aspen Sauna Bench Boards, profile SHP (thermally modified aspen)

Heat-treated aspen bench boards from Thermory, smooth on four sides, with no chemicals added in the process. A 2022 lab study found heat treatment raises formaldehyde and furfural emissions, so we rate it below natural wood.

Best for Builders who want a stable, dark-toned bench board that resists decay and are comfortable with heat-treated rather than plain wood.

Our rating
Fair (3.3 of 5)
Price range
Mid-range
Size
3.5 in wide, 5/4 in (1.1 in actual) or 1 in (0.83 in actual) thick; smooth on four sides with four eased edges; packs of four or five boards, 5 to 10 ft long, depending on the store
Made in
Estonia (made by Thermory in Reola)

approx. $161 for a bundle of four 5.9 ft boards, 5/4 in thick (about $6.84 per linear foot), Finnish Sauna Builders, 2026-10-23

See it on Thermory’s site → (opens in a new tab)

We are not affiliated with Thermory. This link goes to the maker’s own page, with no tracking code. How we're funded.

Also sold at Finnish Sauna Builders ($6.84 per linear foot at 5/4 in ($161.43 for four boards of 5.9 ft)), Sauna Marketplace ($5.70 per linear foot (bundles of four, 5.9 to 9.8 ft)), Haven of Heat ($253 for four 5 ft boards (about $12.65 per linear foot)) .

Reader ratings & reviews

– out of 5

Loading ratings…

Have this product? Please rate it.

    Reviews are personal experiences, not research, and they never change our quality ratings. Every review is read by our team before it appears.

    How we evaluated it

    How it scores Our rating, metric by metric Fair, 3.3 of 5
    1. Materials 45% of the rating 3 of 5

      Aspen heated with steam and no added chemicals, sold plain, but not untreated: a 2022 lab study found heat treatment raises formaldehyde, furfural and acetic acid emissions, and no emissions test of these boards exists. Thermory declares formaldehyde class E1 and its EPD lists no REACH SVHC above 0.1 percent.

    2. Durability 20% of the rating 4 of 5

      Thermory says thermal modification makes wood more stable and rot-resistant, and the benches are surfaced smooth with eased edges; no warranty or test of these boards is stated.

    3. Safety 10% of the rating 3 of 5

      Thermory’s declaration for thermo-aspen cladding gives reaction to fire D-s1,d0 (classified by a notified laboratory) and formaldehyde class E1; the stores give no bench temperature or clearance guidance.

    4. Trust 10% of the rating 4 of 5

      Thermory publishes declarations of performance, a third-party-verified EPD and FSC, PEFC and ISO certificates, and no CPSC recall or Prop 65 notice turned up, but it sells only through resellers whose per-foot prices differ by more than double.

    5. Value 15% of the rating 3 of 5

      About $19.50 to $23.50 per square foot of 5/4 in bench board at Sauna Marketplace and Finnish Sauna Builders (about $43 at Haven of Heat), more than wall wood because it is bench stock.

    The rating, 3.3 of 5, is the weighted average of these scores. See how we rank building a sauna and our standard.

    Where to buy Stores and the prices we saw 3 stores
    • Finnish Sauna Builders (opens in a new tab) approx. $6.84 per linear foot at 5/4 in ($161.43 for four boards of 5.9 ft). Illinois sauna retailer that lists Thermory as a brand. The page does not say which modification level the boards are. We could not confirm it is on Thermory USA’s distributor list.
    • Sauna Marketplace (opens in a new tab) approx. $5.70 per linear foot (bundles of four, 5.9 to 9.8 ft). 1.1 in thick, 3.5 in face. Wood ships for a $795 flat rate per order, free with a heater order.
    • Haven of Heat (opens in a new tab) approx. $253 for four 5 ft boards (about $12.65 per linear foot). 3.5 x 1.1 in, “unoiled”, “chemical-free thermal modification”. More than double the per-foot price of the other two. Packs run 5 to 10 ft.

    Prices as we saw them on October 23, 2026. They change often. These links carry no tracking code and earn us nothing.

    What it’s made of What touches your food, water, skin or air 3 materials
    1. Thermally modified European aspen (Populus tremula), declared by Thermory as cladding “without surface coating” for interior use; Thermory says only heat and steam are used and no chemicals are added
    2. Smooth S4S boards with eased edges; no glue, finish or coating stated (Haven of Heat: “unoiled”)
    3. The modification level is not stated on the board pages. Thermory describes medium (about 190 °C) and intense (215 °C or more) levels and its EPD gives a chamber range of 160 to 220 °C. Thermory USA says its sauna paneling is non-modified or modified at a medium level, while Finnish Sauna Builders’ kit page says its Thermo Aspen is heat-treated at 419 °F (215 °C) or higher
    Who tested it What each test found, and who paid for it 4 tests
    • Paid certification Thermory (declaration of performance T-HB2024-Dv1, EN 14915, system 3; fire class by a notified laboratory) November 14, 2024

      Thermory’s declaration for thermally modified European aspen cladding without surface coating, for interior use: reaction to fire D-s1,d0 (classification report K139_2024 by notified body 2040), formaldehyde class E1, biological durability class 5 (EN 350, the lowest of five classes). Pentachlorophenol and release of other dangerous substances are “NPD” (no performance determined). It is for cladding, not named for bench boards, and says nothing about what the wood gives off when heated. Open ↗ (opens in a new tab)

    • Paid certification EPD Hub (third-party-verified EPD HUB-4824, thermally modified aspen and alder boards) January 9, 2026

      Life-cycle declaration verified on 2026-01-09. It says the boards are dried and thermally modified in chambers at 160 to 220 °C in a chemical-free process, then planed into profiles such as bench boards. It lists raw material from Estonia, Latvia, Lithuania, the UK, Sweden and Ukraine and no REACH SVHC above 0.1 percent, and it says impacts in use were not studied. Open ↗ (opens in a new tab)

    • Paid certification Preferred by Nature (FSC® certificate PBN-COC-009078; PEFC certificate PBN-PEFC-COC-000132) June 8, 2026

      Chain-of-custody certificates for Thermory AS. The FSC certificate (valid to 2030-03-31) lists solid wood boards and sauna products under FSC Mix Credit and says a product counts as FSC only when the claim is on its sales documents; none of the three stores’ pages makes an FSC claim. The PEFC certificate lists no sauna boards. Neither tests what the boards give off. Open ↗ (opens in a new tab)

    • Independent University of Padua and CNR-IBE (lab study of thermally modified wood, not of this product) 2022

      In six species, thermal treatment lowered terpene emissions but raised formic acid, formaldehyde, furfural and acetic acid emissions. It was a lab headspace study, not a sauna, and it gives no exposure levels. Open ↗ (opens in a new tab)

    Who paid, and why it matters
    • Independent The tester took no money from the maker for it: a consumer group, a journalist, a university or a regulator.
    • Paid certification An outside lab or certifier tested or listed it, and the maker paid for that.
    • Maker’s own test A lab report or certificate of analysis the maker commissioned and published.

    A certification is a floor, not a verdict: it checks what its program checks and nothing else. We weigh tests by someone with no stake in the result most.

    What people ask Worries raised online and elsewhere, and what we found 6 questions
    Does heat-treated wood give off more formaldehyde?
    A 2022 lab study of six wood species (PubMed 36227218 (opens in a new tab)) found that thermal treatment cut terpene emissions but raised formic acid, formaldehyde, furfural and acetic acid emissions. It did not test saunas, aspen boards from Thermory or exposure levels, so it cannot say these boards are a problem. Thermory’s own declaration (opens in a new tab) gives formaldehyde class E1 for its thermo-aspen cladding, which is a classification, not a hot-room test. Thermory’s own maintenance page (opens in a new tab) says thermally modified wood “may emit a characteristic scent when the sauna is heated”, which diminishes over time. It is why we score thermo-aspen below natural aspen or alder.
    Are chemicals used to make thermo-aspen?
    Thermory says no. Its thermal modification page (opens in a new tab) says only heat and steam are used and no chemicals are added during modification, its FAQ (opens in a new tab) calls the process non-toxic, and its EPD (opens in a new tab) calls it chemical-free. It adds that oils, paints and other coatings may be added afterwards, so check what you buy.
    How hot is it treated?
    The sources differ. Thermory describes medium modification at about 190 °C for indoor products and intense modification at 215 °C or more, and its EPD gives 160 to 220 °C. Thermory USA (opens in a new tab) says its sauna paneling is non-modified or thermally modified at a medium level, but the Finnish Sauna Builders kit page (opens in a new tab) says its Thermo Aspen is treated at 419 °F (215 °C) or higher. No board page says which level the bench boards are. Ask the store.
    Does the bench get too hot to sit on?
    Thermory says it sells only woods that do not overheat or splinter for sauna boards, and its aspen page lists bench boards among aspen’s uses. We found no measured bench-surface temperature.
    Can I buy it direct from Thermory?
    Not through its main site: Thermory says it supplies exclusively to official distributors and does not sell to private customers, and Thermory USA’s store sells sauna accessories, not boards. One buyer in a 2024 r/Sauna thread (opens in a new tab) says they bought a pallet straight from Thermory, a forum claim we could not check. The three stores we list are resellers; we could not confirm any is on Thermory USA’s distributor list.
    Do the sellers have ties to Thermory?
    Sauna Marketplace says in its own Reddit post (opens in a new tab) that Thermory hosted its first Partner Alliance Summit in Estonia in September 2026 and that it attended, and the store hosts the r/saunamarketplace forum. We found no such statement from the other two stores. Read a retailer’s praise of the brand as a retailer’s.
    Why we chose it What put it on our list 3 points
    • Thermory says the process uses only heat and steam and adds no chemicals, and its third-party-verified EPD calls it chemical-free.
    • Bench stock: 5/4 in boards (1.1 in actual), smooth on four sides with four eased edges, for comfort on skin.
    • Thermory publishes a declaration of performance and a verified EPD that cover its thermally modified aspen.
    Trade-offs What to weigh before you buy 4 points
    • A lab study of heat-treated wood found more formaldehyde, furfural, formic and acetic acid emissions than in untreated wood. It was not a sauna study.
    • The modification level is not stated on the board pages, and the sources differ (medium at about 190 °C, or 215 °C and up).
    • About $19.50 to $23.50 per square foot of bench board at the two cheaper stores, more than natural alder wall boards.
    • Thermory sells only through resellers, the per-foot price differs by more than double between them, and lumber freight can be costly ($795 flat rate at one store).
    What to know Details worth knowing first

    Thermo-aspen is aspen heated with steam until it is darker, more stable and more resistant to decay. Thermory, which makes it, says only heat and steam are used and no chemicals are added, and its verified EPD describes a chemical-free process at 160 to 220 °C. These are bench boards: 5/4 in thick (1.1 in actual), smooth on four sides with eased edges.

    We rate it below plain wood for one reason. A 2022 lab study of six species (PubMed 36227218 (opens in a new tab)) found that heat treatment lowered terpene emissions but raised formic acid, formaldehyde, furfural and acetic acid emissions. It was not a sauna, not Thermory’s boards and gave no exposure levels, so it cannot say these boards are a problem. It does say that “no chemicals added” is not the same as “gives off nothing”. Thermory’s own declaration gives formaldehyde class E1 for its thermo-aspen cladding, but that is a classification, not a hot-room test.

    Ask which modification level you are getting, since the sources differ, and sit on a towel as you would on any bench. Prices differ a lot by store, from $5.70 to $12.65 per foot, and one store adds a $795 flat rate for wood freight.

    What we checked Each claim, and how sure we are of it 6 checks
    Tested by
    Thermory declarations and certificates (fire class, EPD, forest chain of custody); no heated-emissions test
    How Thermory Thermo-Aspen Sauna Bench Boards, profile SHP (thermally modified aspen) measures up against our building a sauna criteria
    What we checked What we found
    Untreated, low-resin wood Maker’s claim Not untreated: thermally modified European aspen (Populus tremula) without surface coating, per Thermory’s declaration. Thermory says only heat and steam are used and no chemicals are added; Haven of Heat says unoiled.
    Species, grade and origin named Maker’s claim Species named in the declaration. Grade and origin are given only for Thermory’s boards in general (“primarily Grade A”, six countries), and the modification level is not stated on the board pages.
    Emissions when hot Not verified No emissions test of these boards. A 2022 lab study of heat-treated wood (not this product) found more formaldehyde, furfural, formic acid and acetic acid than in untreated wood. Thermory declares formaldehyde class E1 for its thermo-aspen cladding, and says thermally modified wood may emit a characteristic scent when heated.
    Environmental declaration (EPD) Verified EPD HUB-4824 for thermally modified aspen and alder boards is third-party verified (2026-01-09). It covers production and end of life and says impacts in use were not studied.
    Forest certificates Maker’s claim The FSC certificate lists solid wood boards and sauna products under FSC Mix Credit; a product is FSC only if the sales documents say so, and the stores do not. We did not check the FSC database.
    Recalls and notices Verified No recall naming Thermory in the US Consumer Product Safety Commission data and no Prop 65 notice in the California Attorney General’s search, both on 2026-10-23. We could not search class actions (the site needs JavaScript).
    What the labels mean
    • Verified We opened an independent record that confirms it: a certifier’s listing, a regulator’s list or a lab report. It is linked under Sources.
    • Maker’s claim The maker says so on its own page or label. We read it but found no independent record.
    • Not verified We looked and could not confirm it, or the maker does not say. Treat it as unknown.
    Sources Where our facts come from 18 sources
    1. Thermory: sauna wall panels and bench boards. Maker’s page. Species, finishes and the distributor-only note. Open ↗ (opens in a new tab)
    2. Thermory: thermal modification. Maker’s page. Heat and steam only; medium about 190 °C and intense 215 °C or more. Open ↗ (opens in a new tab)
    3. Thermory: frequently asked questions. Maker’s page. Calls thermal modification non-toxic and chemical-free. Open ↗ (opens in a new tab)
    4. Thermory: certifications and testing. Maker’s page. Lists the certificates, EPDs and declarations of performance. Open ↗ (opens in a new tab)
    5. Thermory declaration of performance: thermally modified aspen cladding (T-HB2024-Dv1). Maker’s page. Species, fire class D-s1,d0, formaldehyde class E1, system 3. Open ↗ (opens in a new tab)
    6. EPD Hub HUB-4824: Thermory thermally modified aspen and alder boards without surface coating. Test report. Third-party-verified EPD: 160 to 220 °C, chemical-free, raw material origin, no REACH SVHC above 0.1 percent. Open ↗ (opens in a new tab)
    7. Thermory FSC® chain-of-custody certificate PBN-COC-009078. Maker’s page. Scope (solid wood boards, sauna products) under FSC Mix Credit; the claim must be on sales documents. Open ↗ (opens in a new tab)
    8. Thermory: sauna maintenance. Maker’s page. Says thermally modified wood may emit a characteristic scent when the sauna is heated. Open ↗ (opens in a new tab)
    9. Thermory USA: sauna materials. Maker’s page. Sauna paneling is non-modified or thermally modified at a medium level. Open ↗ (opens in a new tab)
    10. r/Sauna: Thermory wood? (2024 thread). Independent source. A buyer says they bought a pallet directly from Thermory; forum posts, not tests. Open ↗ (opens in a new tab)
    11. r/saunamarketplace: We spent three days with Thermory and sauna people from 23 countries (2026 post by the store). Independent source. Sauna Marketplace says Thermory hosted its first Partner Alliance Summit in Estonia. Open ↗ (opens in a new tab)
    12. Finnish Sauna Builders: Thermo Aspen sauna bench boards, profile SHP by Thermory. Independent source. Store price by the foot and by the bundle, and board sizes, seen 2026-10-23. Open ↗ (opens in a new tab)
    13. Sauna Marketplace: Thermory 5/4 SHP Thermo-Aspen sauna bench and floor wood. Independent source. Store price per linear foot and freight terms, seen 2026-10-23. Open ↗ (opens in a new tab)
    14. Haven of Heat: Thermory Thermo-Aspen 5/4 x 4 bench material, 4-board pack. Independent source. Store price by pack and length, “unoiled”, seen 2026-10-23. Open ↗ (opens in a new tab)
    15. Finnish Sauna Builders: Custom Indoor Sauna Room 4 x 6 x 8, pre-cut kit. Independent source. Says its Thermo Aspen is heat-treated at 419 °F or higher. Open ↗ (opens in a new tab)
    16. Exploring volatile organic compound emission from thermally modified wood by PTR-ToF-MS (Romano 2022, PubMed 36227218). Independent source. Six species; thermal treatment lowered terpenes and raised formic acid, formaldehyde, furfural and acetic acid. Open ↗ (opens in a new tab)
    17. US Consumer Product Safety Commission: recall search. Certifier or regulator listing. Returns no recall for Thermory (2026-10-23). Open ↗ (opens in a new tab)
    18. California Attorney General: Proposition 65 60-day notice search for Thermory. Certifier or regulator listing. No matching records (2026-10-23). Open ↗ (opens in a new tab)
    Alternatives Other options to compare 2 options

    Weekly research digest

    New topics and updated research, once a week when there's something new. How it works