You may have heard the term acetylated wood used in the same breath as Accoya. It sounds like something straight out of a science lab — and in some ways, it is. But what exactly is acetylation? And what makes Accoya wood so different from other wood options?

In this guide, we’re peeling back the bark (literally and figuratively) to uncover the cutting-edge technology behind Accoya, from how the acetylation process works to what it means for the durability and sustainability of wood.

What’s the problem with traditional softwood?
What is acetylation?
What is Accoya wood?
How is Accoya wood made?
The acetylation process
Is acetylated wood sustainable?

Before we dive into what acetylation is and why it matters, let’s first understand why timber deteriorates in the first place. There are many causes, but one of the main ones is moisture.

When water gets into the wood cells it can create havoc. It can cause wood to swell, warp, twist and decay. In short, moisture makes wood unstable which could result in sliding windows getting stuck or decking warping.

So, if there was a way to stop water from taking up residence in the wood cells, wood would be more dimensionally stable, resistant to rotting and perform better and for longer. That’s where acetylated wood comes into play.

To explain how acetylated wood works, let’s do a little lateral thinking.

Acetylation is a way of modifying the cellulose molecules in wood cells to prevent the cell walls from absorbing too much water. A good way to try and visualize this is to think of wood as a bundle of drinking straws with the straws representing the cell walls. In traditional softwood, when it rains, water soaks into the straw – the cell walls – and makes the wood swell.

Over time, this constant soaking and drying causes swelling and shrinking which could damage the wood and provides perfect conditions for fungi to flourish.

The chemistry of the acetylation process effectively modifies the molecular structure of the cell walls in wood by yielding molecules that water is not attracted to. With too little water present in the cell walls due to acetylation, fungi cannot live and wood decay cannot occur.

Back to the straws – imagine acetylated wood is made from a bunch of drinking straws where the straw material doesn’t allow water to be absorbed. Water can flow through the straws but it cannot penetrate the walls of the straw.

So, acetylated wood can get wet as the water flows through the straws, aka the cell walls, but equally it then dries out without ever creating an effective environment for fungi to live and grow.

To prevent the swelling and shrinking from happening, the precise acetylation process to create Accoya introduces a highly concentrated form of vinegar called acetic anhydride. Just the right amount of heat and pressure is then applied to change the wood at a cellular level.

What happens is a chemical reaction causing the water-loving hydroxyl groups to transform into durable water-resistant acetyl groups in the cellulose molecules in the wood cells.

By reducing the wood’s ability to absorb water by 80% compared to untreated timber, swelling and shrinkage is drastically reduced, increasing the wood’s long-term dimensional stability and structural integrity.

Not only that, the change in structure of acetylated wood means that most fungi causing wood rot cannot live and grow in the Accoya, and therefore cannot cause wood decay.

Finally, most termites don’t recognize Accoya wood as a food source, which further reduces the risk of decay.