Question

when water increase in wood above the fiber saturation point the process leads to swelling ?

Answer 1

Yes, that is correct. When water content in wood increases above the fiber saturation point, the wood fibers swell. This is because wood has an inherent ability to absorb and release moisture from its environment. When it absorbs water beyond the fiber saturation point, the cell walls of the wood fibers start to expand, causing the wood to swell.