It is well known that chemical modifications to improve decay resistance also reduce the equilibrium moisture content (EMC) of wood. The mechanism of this action, however, has been the subject of much debate. Several groups have suggested that decay resistance is a result of lower diffusion rates of fungal degradation agents through the wood cell wall. A recent paper explained the fundamental principles governing diffusion through the wood cell wall. This current paper summarizes the findings in that paper with respect to decay resistance of modified wood. In short, large scale motions of the amorphous polysaccharides of the wood cell wall are necessary for diffusion of degradation agents during incipient decay. Many wood modifications are likely preventing decay by preventing these motions. Water promotes large scale motions of cell wall polysaccharides by increasing free volume, increasing the distance between polymer chains, and reducing the number of hydrogen bonds between polymer chains.

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