Thermo ash, or thermally modified ash, is ash wood that has been subjected to a heat treatment process (typically 180-220°C or even up to 240°C) in a low-oxygen environment using steam. This process alters the wood's chemical and physical properties, making it more durable and resistant to decay, insects, and moisture.

Key features and advantages Enhanced durability: Thermo ash has increased resistance to rot, decay, and insect infestation, leading to a longer lifespan compared to untreated wood. Its durability is often compared to tropical hardwoods and is rated as Durability Class 1 (25+ years' protection against wood decay). Exceptional dimensional stability: The thermal modification process minimizes shrinkage, swelling, and warping due to changes in humidity and temperature. This makes it a reliable choice for outdoor applications in areas with varying climates. Natural resistance to decay and pests: The heat treatment modifies the organic compounds in the wood, making it less attractive to termites and fungi and reducing the need for chemical treatments. Attractive aesthetic: Thermo ash gains a deeper, richer brown tone during the thermal modification process, similar to some exotic hardwoods. Its appearance can be maintained with UV-protective oiling or allowed to naturally weather to a silver-gray patina.