Thermory Saunas & Sauna Wood

Thermory is an Estonian company that makes thermally modified wood, sauna materials and sauna kits, and it describes itself as the world’s largest producer of thermally modified wood and sauna materials. For saunas it makes wall paneling, bench boards, trim, doors and outdoor kits like the barrels, the Sauna Squares and the Luik. It also owns Auroom, which builds indoor and outdoor sauna rooms with Thermory wood.

Thermory wood is made in Estonia. Sauna boards, benches and doors come from Thermory’s Reola plant, which Thermory calls the world’s largest producer of sauna materials, and exterior cladding and decking come from its Loo plant. We walked both in September 2026.

Thermally modified wood has been changed by heat and steam, not chemicals, so it swells and shrinks far less with humidity. Thermory runs it as a precisely controlled process in large kilns: the wood is dried to zero moisture over 35 to 46 hours, brought to an exact temperature under steam (374°F for medium modification, 419°F or more for intense), then cooled and brought back to a stable moisture level. The color goes all the way through.

No. Thermory modifies its wood with heat and steam only. Nothing is sprayed on or pressed in, and the brown color is the wood itself, not a stain.

Thermory checks its boards at several points and pulls the ones that miss its standard. At the Reola plant a Microtec Goldeneye 500 X-rays and 3D-scans every board for moisture and curvature before it is modified, and after profiling a second line checks the boards with eight 3D cameras and a dimensional control system. Products are also tested outdoors for years at the Loo plant before they are sold.

New Thermory wood has a mild, toasty scent, not a burnt one, and it is much quieter than cedar. The scent fades with use, faster if you heat the sauna often. If scent matters to you, order a free sample and smell it first.

For most saunas we recommend Thermo-Aspen: it is smooth, has very few knots and gives a clean, modern room. Thermo-Spruce is the rustic, knotty look at a lower price per foot, and alder has a fine, even grain that many people love for benches. A popular budget mix is Thermo-Spruce on the walls and ceiling with Thermo-Aspen benches. Order free samples of two or three and look at them in your own light.

For the walls and benches of a sauna, we recommend thermally modified wood like Thermory over cedar. It barely moves with heat and humidity, so the joints stay tight over years of heating and cooling. Traditional Finnish saunas also favor quieter-smelling woods like spruce, aspen and alder, so the room smells of the steam and whatever you add to the water rather than the wood.

Yes. Thermo-Spruce has tight knots, and that is its rustic character and part of why it costs less. If you want a clean, knot-free wall, choose Thermo-Aspen or Thermo-Magnolia instead.

They are the same species at three levels of Thermory’s process. Natural alder is not modified and is the lightest. Thermo-Alder gets a medium modification that peaks at 374°F and turns a warm medium brown; it is for indoor use. Dark Thermo-Alder gets an intense modification at 419°F or more and is the deepest brown. Samples side by side settle it quickly.

Yes, if it is finished for the hot room. For a black interior, use a board finished black for sauna use, like our brushed and waxed black Thermo-Spruce. Thermory’s painted and embossed black boards are exterior cladding, not sauna paneling. The Thermory Ignite barrel is black on the outside and natural wood inside.

For benches we recommend 5/4 SHP bench boards in Thermo-Aspen or Thermo-Alder. The thicker 5/4 board is stiffer than a 1x4, needs fewer supports and can be sanded back to new after years of use. Thermo-Spruce 5/4 is the budget bench and floor board, and Thermo-Magnolia comes as an extra-wide bench board.

Thermory sauna wood doesn’t need a sealer to hold up, but Thermory’s care guide does ask you to treat it. The guide calls for a sauna-safe product on the wood at least once a year, more often if you heat the sauna a lot, and the warranty expects you to follow it. Paraffin oil on the benches and sauna wax on the walls are the usual picks, and a towel on the bench does the rest. Never use regular stain or paint inside the hot room.

You don’t have to. Unfinished Thermory wood holds up outdoors and weathers to a soft silver-gray in the sun, which you can see on Thermory’s own weathering wall. To keep the brown color, apply a breathable exterior oil with UV protection within about a week of assembly and renew it every year.

Either works. Thermory’s installation guide covers both. Leave an air gap behind the paneling by fastening it to furring strips that run perpendicular to the boards, over the foil vapor barrier. When the boards run horizontally, the tongue points up.

Use stainless steel fasteners only. Thermory’s installation guide calls for stainless staples driven through the groove side, so each fastener is hidden by the next board.

Work from face coverage, not nominal size: a 1x4 STS4 board covers about 3.1 inches of wall once the tongue locks, a 1x5 about 4.3 inches, and wide Thermo-Magnolia 5.4 to 6.4 inches. Paneling comes in bundles of six boards of one length (bench boards in fours), and lengths are metric conversions, so a 5.9 ft board is 70.8 inches. Round up to the next length. Send us your room size and we’ll check the count with you, or lay the room out in SaunaDesignPro, our free 3D sauna design tool.

Choose the barrel for a compact, traditional sauna and the Sauna Square for more room. The barrel’s round shape keeps the space tight around you. The Square has an L-shaped bench on two levels, a porch and a big glass front, and comes in medium and large sizes for couples, families or groups. Plan how a large Square will be unloaded on delivery day.

Set a Thermory sauna on a firm, level base that keeps it up off the ground: concrete, pavers or compacted crushed stone. Thermory’s warranty doesn’t cover a sauna set directly on gravel, grass or mud, and a base that isn’t level can keep the door from closing properly. We built our No 60 barrel on compacted gravel with leveled 12 x 12 inch pavers, then checked for gaps with a stave both ways.

You choose the heater with your Thermory sauna when you order it here, sized to the model, and it ships separately. In the barrels we most often pair a Harvia KIP, HUUM DROP or HUUM HIVE. In the Sauna Squares, the HUUM HIVE Mini gives the most top heat, a Harvia Virta keeps it simple, and a Saunum Air Perfect gives the most even heat and fits if you trim the floor grid. Skip a heater that hangs on the wall of a Square: the wall curves into the floor, so it sits too high to warm the lower bench. We tested one in Ben Frizzell’s. Glass counts as extra volume, so tell us your model and we’ll size the heater and the circuit.

Thermory’s manuals for its barrels and Squares set the maximum room temperature at 194°F and warn that going higher can overheat the sauna. We size the heater so you get there comfortably, not so it can push past the cap.

No. A Thermory barrel is solid thermally modified wood with no insulation layer: 1.65-inch staves and tempered glass. A solid back wall holds heat better than the panoramic window, and we count the glass when we size the heater.

Thermory barrels ship with a fitted rain jacket, and Thermory designs it to stay on all year: it sheds water and keeps condensation from dripping inside. Some owners later add asphalt shingles or a metal roof with a drip edge to match the house. Clear heavy snow off the roof without tearing the jacket.

A Thermory barrel or Square takes two people a full day to a weekend on a level base. Ben Frizzell built his Square in about a day, and our No 60 barrel mostly on his own over three days, a few hours at a time; with two people he figures six to eight hours. The build videos above walk through every step.

A Thermory sauna can go in a rental, but check the warranty first. Thermory’s current sauna warranty excludes public and rental saunas unless Thermory agrees in advance, so tell us before you order and we’ll ask them for you.

Thermory’s current sauna warranty (2024) covers the first buyer for two years against defects in construction, manufacturing and materials, and against rot on the outside that makes the sauna unusable. It expects you to follow Thermory’s installation and care instructions, and it doesn’t cover a sauna set directly on gravel, grass or mud, or a public or rental sauna unless Thermory agrees in advance. Heaters, lights, electrical parts and glass fall under their own makers. Read Thermory’s sauna warranty.

We check stock in real time across Thermory’s three US warehouses, in New York, Texas and Colorado, for every kit and for sauna wood down to the length of each board. Tell us what you’re after and we’ll confirm what’s on the shelf, which warehouse it ships from and when it should reach you. The heater usually ships separately.

Shorter boards can often ship by parcel, which is gentler and costs less, while longer boards and saunas go by truck freight. We quote shipping to your address before you order, and we size board lengths so ends that take a knock in transit can be trimmed.

Yes. Every Thermory wall and bench board on this page has a free sample option: pick the per-foot option on the product page, or ask us and we’ll send a few species. Color varies a little from lot to lot, so treat a sample as a guide rather than an exact match.

Yes. Thermory lists Sauna Marketplace on its own sauna dealer page.