Water occurs in wood in two places, First, theirs the free water that fills the inside of the wood cells. That's like water in a bucket. Second, water also infiltrates the cell walls. That's called bound water. Imagine squeezing a piece of cotton Cheeses cloth until all the free water is drained away. The cloth though, remains damp because the material continues to contain moisture-the bound water.
When wood contains bound water its is said to be in its fiber saturation point. And the bound water can be eliminated completely only by drying it. Somewhere with no relative humidity, as in an air-tight oven.
Wood likes water, wood rates as a hygroscopic substance. Thai is it has ans affinity for water and readily absorbs it as a liquid and vapor. This ability directly deepens on the humidity of the surrounding atmosphere. therefore the amount of moisture is wood changes as the humidity changes.
The term Kiln-Dried means that wood moisture was removed in a chamber where air circulation, humidity and temperature were controlled.