It is generally understood that diffusion through solid polymers including wood depends on molecular motions of the polymer, free volume in the polymer matrix, diffusant dimensions, and solubility of the diffusant in the polymer matrix . Diffusant transport is generally controlled by the motion of similar-sized features of the polymer matrix. Smaller diffusants, such as water molecules, are controlled by uncoordinated local motions, whereas larger chemicals, like mineral ions, are controlled by cooperative motions. As a hygroscopic material, water absorbs in the cell wall and acts as plasticizer that increases molecular motions and free volume. It is generally understood that diffusion is promoted by increases in water plasticization. Of particular interest is an ambient temperature moistureinduced glass transition that current evidence indicates occurs in the amorphous polysaccharides when wood is conditioned between 50 and 85% RH, which corresponds to 10-15% moisture content. Diffusion of larger chemicals, like mineral ions, are only expected to appreciably occur through rubbery polymers above their glass transition that have cooperative motions.