Accoya is a name given to a timber that has gone through the process of acetylation. In essence, this alters the cell structure of wood making it stronger and more durable.Primarily, Radiata Pine is used, which is generally grown on plantations in Australia and New Zealand. It is a quick growing tree with a straight grain and very few knots or resin pockets. Due to the global demand for hardwoods, chosen in the past for their durability, and the declining global stock available, Accoya is now coming into its own as the way forward. 

All wood contain ‘free hydroxyl groups’: that’s hydrogen and oxygen within each cell. These hydroxyl groups release and absorb water depending on environmental conditions and this constant process of absorption and release breaks down the cells thus enabling rot to take hold. That’s why we either paint or stain wood to create a barrier between the wood and the outside to try and keep this absorption and release process to a minimum. With acetylation, ‘acetyl groups’ are introduced, changing the hydroxyl groups. Acetyl is created from Acetic Anhydride, i.e. vinegar – but not the sort that one would use in the kitchen.So in the simplest of terms, acetylation is subjecting a softwood (Radiata Pine) to vinegar (Acetic Anhydride), which turns it into a hardwood by preventing the cells in the wood from being able to absorb water. The wood is pickled.
The benefits are extraordinary. 

1  The process penetrates 100% of the wood, not just the outside; it’s not an envelope treatment.

2  It is 100% environmentally sound – no nasty chemicals, tars, or metals – and is FSC Certified.

3  It can be overpainted or stained and because of its stability the paint or stain you put on lasts a lot longer.

4 It can be used in all exterior joinery applications.

5 It remains stable. It is far less prone to warp and has virtually no swelling or shrinkage issues.

And this is the big one: 6 It has a 50year guarantee against rot; that’s 50 years without painting or staining. 

It has a 25 years guarantee against rot below ground, without painting or staining. The other great thing about Accoya is that it is now in an MDF, so sheet material from 6mm to 18mm is now available with the same benefits mentioned above.In my opinion this is the future of timber. It has now become possible to have a truly sustainable product with advanced durability.