Accoya is a brand name for a high-performance modified wood product.

It is made from fast-growing, sustainably-sourced softwood (specifically Pinus radiata a.k.a. radiata pine).

The key process is acetylation: wood is treated so that the wood’s free hydroxyl (-OH) groups – which attract water – are converted into acetyl groups, reducing the wood’s ability to absorb water.

Because of this modification, Accoya offers much greater dimensional stability, durability and environmental credentials compared to many untreated or conventionally treated timbers.

Here are some of the standout features:

Durability: Accoya is rated Class 1 in durability (the highest grade) and comes with warranties of ~50-years for above ground use and ~25-years for in-ground/freshwater use.

Dimensional Stability: Swelling and shrinking are substantially reduced compared to regular softwoods. It helps maintain straightness, flatness, and reduces warping/cupping.

Environmental / Sustainability: Because it uses fast-growing softwoods, is non-toxic, 100% recyclable and has strong green credentials.

Workability & Finish: The acetylation process does not weaken the wood—in fact the performance (e.g., hardness) can be improved—so it retains good machinability and is compatible with standard coatings and finishes.

Coatings & Maintenance: Because of the stability, coatings last longer. For example, some trials indicate a 3-4x increase in coating life before maintenance is needed.

Accoya is used for a wide variety of applications, particularly where durability, weather-exposure and stability are critical:

Windows & doors (especially in demanding climates)

Exterior cladding and siding

Decking and outdoor flooring

Structural or semi-structural uses: bridges, water exposure, canal linings etc.

Interior where moisture stability is important (though many use it externally)