About ThermoAspen

Who publishes ThermoAspen.com

We are Sauna Marketplace, a US retailer at saunamarketplace.com. We sell thermo-aspen, including Thermory products, so we cite every figure to the page it came from. Check any number before you order.

The wall profiles and shop links on this site lead to thermo-aspen we sell.

Why the site exists

The figures you need to plan a thermo-aspen sauna sit in long technical PDFs. The ThermoWood® Handbook (International ThermoWood Association, 2026) alone runs 68 pages, with its values in metric. ITWA handbook

This site pulls out the figures that change your build, converts them to US units, and links each one to its page. Covering width is one example: Thermory's catalog lists it in millimeters, and the linear feet you order depend on it. Thermory catalog, p. 8

Each main page answers one kind of planning question:

• How it's made covers the kiln process, product classes, and temperatures.
• Wall profiles compares profile shapes and installed coverage.
• The spec guide covers claim checks, quantity math, and installation.
• The buyer's guide walks through choosing, estimating, framing, and finishing in four steps.
• The questions page and the blog answer single questions with sources.

Three rules behind every page

Three rules decide what goes on a page and which document each figure comes from.

1. Start from the document that made the claim.

   Figures come from a manufacturer catalog or installation guide, the ThermoWood® Handbook, or USDA wood research. Forum threads and store listings can raise a question; a primary document answers it.

2. Handbook data stays with what was tested.

   Test figures come from ITWA's handbook, mostly on pine and spruce. For Thermory boards, use Thermory's catalog. Each handbook figure keeps its species label and is never presented as a value measured on aspen or as the specification of a board you can buy here.

3. For your build, the product's own document decides.

   Board size, covering width, fastening, and care come from the current document for the exact product. Check that document before you cut or order.

How pages are sourced and checked

Primary documents first

These are the documents behind every figure you read here. Each link opens the publisher's own copy.

Every figure tagged to its source

Each figure carries a citation tag that links to its source. For paged PDFs, the tag opens the cited page. For example, the ITWA definition sets 320°F as the minimum temperature for thermal modification. ITWA handbook, p. 4

Handbook values come from the 2026 Swedish edition. Terms follow the 2025 English edition, which uses the same page numbers and the same data, apart from the production chart on p. 5. ITWA handbook (English)Thermory USA's installation guide prints no page numbers, so its tags give the PDF page.

US units, rounded in the safe direction

European sources give metric values, and you see only the converted US figure. Build limits appear as fractions of an inch, with minimums rounded up and maximums rounded down, so a conversion never loosens a limit.

The handbook's sauna drawings for ThermoWood® panels show why. The ventilated gap behind the panels converts to at least 13/16 in, and batten spacing to no more than 23-1/2 in. ITWA handbook, p. 38 Battens at 16 in on center meet that limit, and battens at 24 in on center do not.

Thermory USA's guide already uses inches but prints them as decimals. Its figures appear as fractions too, rounded the same way, so you read the same limit on every page. Thermory USA guide, p. 2

Handbook data, scoped to what was tested

The handbook sorts ThermoWood® products into two classes. Thermo-S stands for stability. Thermo-D stands for durability, meaning stability plus resistance to decay and weather. ITWA handbook, p. 18

Aspen appears in the handbook's species table in both classes. ITWA handbook, p. 9 Beyond that listing and a chart of typical raw timber sizes, the handbook reports no test data measured on aspen. Its Thermo-D temperature table has no aspen row, so you will find no aspen Thermo-D temperature here. ITWA handbook, pp. 10, 18

Where a value was measured on pine or spruce, the page names the species.

Each maker's documents cover its own products

Thermory documents its own process. For sauna materials, its catalog describes a high-pressure chamber that heats the wood up to 356°F while pressure rises to about 130 psi. Thermory catalog, p. 6

Pages about Thermory thermo-aspen take dimensions, grading, installation, and care from Thermory documents, and the same rule applies to any other maker's product. Price, stock, and shipping change, so check them on the live Sauna Marketplace product page.

Who ran the tests

Where a source names the lab behind a test, the page names it too. The handbook's emissions figures, for example, come from VTT, the Technical Research Centre of Finland, which measured the pine samples. ITWA handbook, p. 30

Photos, drawings, and credits

Manufacturer photos name the manufacturer, and the photographer where one is known. Photos and video we shot carry a Sauna Marketplace credit.

No photo or figure from the ThermoWood® Handbook appears on this site. Where a page restates handbook values, it rebuilds them as a new table or chart, in US units, and cites the page.

A project photo shows one room under one set of lights. Thermory's catalog notes that actual products may differ in appearance, since wood is a natural material. Thermory catalog, p. 8 Look at a physical sample under your own lights before you order for the room. Order a sample of STS4 thermo-aspen.

Trademark notice

The handbook defines ThermoWood® as a registered trademark that only association members may use. ITWA handbook, p. 4 On this site, the name refers to the handbook and to the ThermoWood® products it describes.

For the process itself, pages use the generic terms: thermal modification, thermally modified aspen, or thermo-aspen.

Our relationship with Thermory

We sell Thermory products, including Thermory thermo-aspen. Thermory makes them, and Thermory's documents are the reference for their specifications.

If this site and a current Thermory document differ, follow the Thermory document for the Thermory product, then tell us so the page can be corrected.

Thermory USA posts profile drawings and installation documents on its downloads page. The Thermory products we sell are listed on the Sauna Marketplace Thermory brand page.

Report an error

Send corrections through the Sauna Marketplace contact form. A report is quickest to check when it includes:

• The page address and the sentence or figure you think is wrong.
• The document, edition, and page that show the correct value.
• Any citation tag that opened the wrong page or a missing file.

Each report is checked against the cited source, and the page is corrected when the source supports the change. Makers revise their documents, so a note that a newer edition exists helps too.