Thermally Modified Wood

What is Thermally Modified Wood

Thermally modified wood is a high-quality wood product created through a controlled heat treatment process. This process enhances the wood’s properties, making it more durable, stable, and resistant to biological decay. Originating in Finland, the thermally modified wood process is now globally recognized and utilized, with the International Thermowood Association overseeing the standards and promotion of these products, the brand ThermoWood® may only be used by the members of the Association.

The Thermally Modified Wood Process

Thermal modification involves heating wood to temperatures between 160°C and 230°C in the absence of oxygen. This treatment alters the wood’s chemical and physical properties, enhancing its durability and stability. The process is divided into several phases:

  1. Initial Heating: Wood is heated gradually to remove moisture.
  2. Thermal Treatment: The temperature is raised to the desired level, altering the wood’s chemical structure.
  3. Cooling and Conditioning: The wood is cooled and re-moisturized to balance its moisture content.

Advantages of Thermally Modified Wood

Thermally modified wood offers numerous benefits compared to untreated wood:

  1. Durability: Enhanced resistance to biological decay, making it suitable for outdoor use without chemical preservatives.
  2. Dimensional Stability: Reduced swelling and shrinkage due to moisture, ensuring the wood retains its shape and size.
  3. Environmental Benefits: No chemicals are used in the process, and the wood is fully recyclable.
  4. Aesthetic Appeal: Rich, uniform color that can be maintained or allowed to develop a natural patina over time.
  5. Reduced Thermal Conductivity: Improved insulation properties, making it suitable for use in energy-efficient buildings.

Applications of Thermally Modified Wood

Thermally modified wood is versatile and can be used in various applications, including:

  1. Cladding: Exterior and interior wall cladding due to its durability and aesthetic appeal.
  2. Decking: Ideal for outdoor decking, offering long-term resistance to weather and wear.
  3. Furniture: Suitable for both indoor and outdoor furniture, combining durability with a beautiful finish.
  4. Saunas: Commonly used in sauna construction due to its low thermal conductivity and resistance to moisture.

Environmental Impact

Thermally modified wood is an eco-friendly product, as it is made from sustainably sourced timber and does not involve the use of harmful chemicals. The process enhances the wood’s lifecycle, reducing the need for replacement and thereby conserving natural resources.

Quality and Standards

The International Thermowood Association ensures that all thermally modified wood products meet strict quality standards. Members of the association must adhere to a rigorous quality control system, ensuring consistent product performance.


Thermally modified wood represents a significant advancement in wood treatment technology, offering enhanced performance, environmental benefits, and aesthetic appeal. Its applications are vast, making it a preferred choice for architects, builders, and homeowners looking for a durable and sustainable wood product.

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