Thermally modified wood – what is it?

Thermally modified wood, often referred to as thermowood, is real wood enhanced using only heat and steam to improve its durability, dimensional stability, and resistance to decay. It offers architects and builders chemical free, sustainable, and high-performance wood products that are suitable for various applications.

In addition to increasing its durability, thermal modification adds a number of properties to the wood that make it a highly sought-after building material. With improved dimensional stability, the wood will stop reacting to changes in humidity, which is why it is an excellent material for exterior cladding, decking, saunas and underfloor heating.

The wood simply absorbs less moisture than unmodified wood; it has a reduced risk of mildew and mould, and it endures heat better. All this while retaining the natural properties of wood with several improved features, including a beautifully deep and even tone.

How is Thermory thermowood made? Like baking bread

Thermory thermowood production

Thermal modification is a bit like baking bread. The process takes place in a specially designed oven – a thermokiln, where sensors send information into computers that are constantly monitored by thermal modification specialists.

In order to assure the highest quality, Thermory uses a special thermal modification formula, which is the result of over 20 years of hard work and experience.

However, all thermal modification producers follow the same principle: within max 48 hours the temperature of the wood is raised up to 215 degrees, reducing the equilibrium moisture content, which is followed by a cooling process. No chemicals are used in the process, only heat and steam.

The high heat alters the wood’s cellular structure, reducing its moisture content and eliminating natural sugars that can attract pests and promote decay.

A big part of our thermowood quality comes from meticulous sourcing of raw material. We buy lumber that meets the strictest criteria, backed by decades of cooperation with top forestry companies supplying high-end wood species, ultimately resulting in superior-quality products. 

Thermory has a refined process to thermally modify various wood species

oak: an exclusive hardwood with inherent beauty and sophistication

ash: a high-performance hardwood that exceeds expectations

pine: the new durability standard for softwood

spruce: a durable softwood with natural charm

radiata pine: an elegant, knot-free look in durable softwood

magnolia: creamy and golden wood that offers a luxurious finish

aspen: a smooth, attractive wood with a characteristic light tone

alder: the perfect sauna material – hardy, water repellent and doesn’t overheat

Read more about the wood species

Main benefits of thermowood 

Thermal modification enhances the wood uniformly, ensuring consistent properties throughout each board. This way the wood performs exceptionally well in both exterior and interior settings and is valued for its appearance, durability and stability even in challenging climates, low maintenance needs, and long lifecycle. 

Durability

Thermowood is less susceptible to insect damage, as the modification process removes the sugars that typically attract pests, making it ideal for outdoor applications. Here you can read more about wood durability.

Dimensional Stability 

With reduced moisture absorption, thermowood resists warping, cupping, and swelling, ensuring architectural precision is preserved over time.

Non-toxic 

Thermally modified wood contains no added chemicals, making it safe to handle and suitable for environmentally conscious projects.

Low Maintenance 

Unlike traditional wood, thermowood does not require constant sealing or treatment. It performs well untreated, and color treatments are optional based on aesthetic goals.

Aesthetic considerations and maintenance 

Thermory Benchmark thermo-ash cladding

Thermowood is visually stunning, with deep, rich tones ranging from chocolate browns in red oak to warm golden hues in pine. Its smooth surface and uniform color give it a refined, modern look ideal for architectural cladding, decking, and interiors.

Over time, exposure to UV rays causes the wood to naturally fade to a silvery-gray patinaa feature many architects embrace as the change in color does not compromise the performance of the wood.

If color retention is desired, UV-resistant oils or stains can be applied. This flexibility gives designers control over how the material weathers and ages. Find out more about wood treatments that Thermory offers.

Installation and handling 

Thermowood is installed like conventional timber but its higher stability makes it easier to work with in architectural details.

Because thermally modified wood is more stable – it expands and contracts less with changes in humidity or temperature compared to untreated wood, it is suitable for precise applications. It helps ensure that:

  • Cladding lines remain straight and flush
  • Decking boards don’t warp or gap unevenly over time
  • Custom profiles and joints align cleanly

Read more about Thermory thermowood installation.

Thermowood applications in projects 

Thermory thermowood’s versatility makes it suitable for a wide range of architectural and design applications. Whether in residential, commercial, or public projects, its performance, aesthetics, and adaptability make it a reliable material for both indoor and outdoor use. Take a look at Thermory projects from all around the world.

Private house, Thermory Benchmark thermo radiata pine cladding

Residential Architecture

Thermally modified wood is often used for exterior cladding, decking, fencing, and even interior paneling in private homes. It brings warmth, character, and durability to modern and traditional architectural styles alike. Its natural weathering process and minimal maintenance requirements make it ideal for homeowners seeking long-lasting beauty with low upkeep. 

Health Center in Ülemiste, Thermory Benchmark thermo-pine cladding, architects Apex AB, Ingrid Kaur, Ristjan Johanson, photo. Olev Mihkelmaa

Commercial Environments

In commercial spaces, such as restaurants, hotels, retail spaces, or offices, thermowood offers a sophisticated, natural appearance that performs well under frequent use and changing weather. Its ability to retain its form and appearance over time, with minimal maintenance, makes it especially appealing for high-visibility spaces that demand lasting performance and visual impact. 

Centro Arte Moderna Gulbenkian, Portugal, Thermory thermo-ash ceiling D4, Architect Kengo Kuma & Associates, Photo Fernando Guerra

Public and Urban Spaces

Thermowood is commonly used in parks, boardwalks, façades of public buildings, and other urban infrastructure. Its ability to withstand exposure to the elements and environmental fluctuations ensures reliable long-term performance in urban spaces. 

Office sauna in Estonia, Thermory thermo-aspen wall panels and benches, Photo. Karl Kasepõld

Wellness Spaces and Interiors

Due to its resistance to heat and humidity, thermally modified wood is also a preferred material in saunas, spas, and wellness environments. It is smooth to the touch, comfortable underfoot, and naturally insulating.

Sustainability and certifications

Thermory’s commitment to sustainability is reflected in both material sourcing and life cycle impact of wood products:

  • Nordic Swan Ecolabel, FSC® and PEFC™ certified raw materials ensure responsible forestry
  • Thermal modification eliminates the need for chemicals
  • Long service life and low maintenance reduce environmental cost over time
Private Time House, Estonia, arhitekt_KMK Stuudio and Web Systems OÜ, Photo. Kroot Tarkmeel

We have assessed the life cycle of our products and have Environmental Product Declarations (EPD) for both natural and thermally modified wood.

Thermally modified wood binds four times more CO2 than is released during its production, helping to reduce the construction sector’s climate impact when used as a substitute for high-CO2 materials like concrete and steel.

Sourced from sustainably managed forests, thermowood is an environmentally conscious  alternative to exotic hardwoods, reducing pressure on endangered tropical forests. Especially now with the CITES regulations on ipe and cumaru.

Pricing and availability 

While the initial cost of thermowood is generally higher than untreated softwoods, it offers excellent long-term value due to its durability, reduced maintenance needs, and superior dimensional stability.

Factors influencing pricing:

  • Wood species: Red oak and ash tend to be premium options
  • Profile complexity: Custom profiles or hidden fastener systems may add cost
  • Project size: Volume discounts available for large-scale developments

Thermory provides a broad selection of thermally modified products suited for both exterior and interior applications. With an established international network of distributors and resellers, Thermory products are widely accessible and supported by technical expertise, samples, and specification guidance for architects and builders. Find your nearest distributor.

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