Distance from Water ( Å) 0 3 6 12 ∞ % Hydroxyl Groups Acetylated 0 29 54 82 100 % dry weight gain (WPG%) 0 5 10 15 18 refers to the volume expansion that takes place. The "constant" system removes water upon acetylation to maintain a constant volume, thereby reducing the moisture content to that seen in acetylated cell walls. Removing additional water, reduces the size of the acetylated system by 2.6 %, compared to the starting unacetylated model. Table lists the system size with the adjusted water weight, or the number of water molecules removed for each % dry weight gain after acetylation for the "constant" systems. As the dry weight increases, using equation 2, a larger number of water molecules are removed from the system, such that the 18 WPG % acetylated cell wall contains about 19 % water weight (Table ).