The Process
The wood you see on this site travels about 4,500 miles from forest to finished board. Every mile of that journey matters to how it performs on your building. Here's the full sequence.
1. The forest
Our raw material Nordic pine, radiata, ayous, and aspen is sourced from responsibly managed forests via SWM Wood's supply chain in Finland and their partner mills. Finnish forestry is among the most regulated in the world, with harvest volumes legally capped well below annual growth and with chain-of-custody tracking from stump to kiln.
2. Cutting and drying
Sawn logs arrive at SWM Wood's mill in Mikkeli, a small city on the Saimaa lake system in southeastern Finland. The boards are rough-cut to slightly oversize dimensions and kiln-dried to approximately 14% moisture content, the starting point for thermal modification.
3. Thermal modification
The treated boards enter SWM Wood's ThermoWood kilns. The process takes roughly 72 hours from end to end, with three controlled phases:
Phase 1 High-temperature drying
The kiln is heated to 130 °C. Remaining moisture evaporates and ventilates out of the chamber as steam. At the end of this phase, moisture content has dropped to near zero.
Phase 2 Thermal modification
Temperature rises to between 185 °C and 215 °C, depending on the specification (Thermo-S, Thermo-D, or Thermally Modified Timber). Steam is continuously introduced to prevent ignition at these temperatures wood is normally combustible above 300 °C, but in an oxygen-deprived steam atmosphere it remains stable.
During this phase, the chemistry of the wood permanently changes. Hemicellulose, the sugar compound fungi need to cause decay caramelizes and is rendered inedible to microorganisms. Free hydroxyl groups along the cellulose chain are reduced, which dramatically lowers the wood's affinity for water. The result: a board that doesn't rot, doesn't absorb water, and doesn't swell or shrink through humidity cycles.
Phase 3 Cooling and re-moisturizing
The kiln cools under continuous steam, bringing moisture content back up to a stable 4-6%. The result is structurally stable, biologically inert, dimensionally predictable wood ready to travel.
4. Atlantic transit
Treated boards are crated and shipped by ocean freight from Finland to the port of Charleston, South Carolina. From Charleston it's a short truck ride inland to our facility in Greenville.
5. Greenville milling
This is where the material becomes the profiles you see on the site. We mill every board at our Greenville facility to our own tooling the TG-I, TG-U, TG-V, TG-W, TG-STriple, TG-Lap, RS60, D1, D1-HF, D1-AS, and D1-AS2 profiles and cut to length.
Doing the milling in the US lets us control profile consistency directly and respond quickly when architects need custom dimensions or special runs.
6. Delivery
Finished product ships from Greenville by LTL freight to projects across the United States and Canada. Typical door-to-door time is 2-4 weeks from order confirmation.
What makes this different
Most Thermowood in North America arrives through a long chain of intermediaries: Finnish mill - European importer - North American distributor - regional rep - lumber yard - contractor - project. Each hand adds margin, and nobody along the way has direct accountability for the finished milled profile.
Thermosticks collapses that chain to three steps: Finland treats, Greenville mills, you receive. We can guarantee consistent profile geometry because we cut it ourselves. We can answer technical questions because we see every board before it ships. And we can price honestly because the middle markups don't exist.
The environmental ledger
Thermowood's environmental profile is strong by any wood-product standard:
- Chemical-free process; only heat and steam are used
- No toxic waste; the only kiln emissions are water vapor and trace wood extractives
- Biogenic carbon stored in the material for the life of the building
- Full end-of-life compostability or biomass use
- Chain-of-custody documentation available on every order
A full Environmental Product Declaration for the ThermoWood process is maintained by the International ThermoWood Association and is available on request.