Why does wood swell when wet?
Show answer & explanation
Answer: Water fills wood cell walls
Water fills wood cell walls ✓ — Correct! Wood is made of cellulose fibers with cell walls that absorb water molecules through hydrogen bonding. As water molecules enter the cell walls, they push fibers apart, causing wood to expand (swell). When it dries, water leaves and wood shrinks—that's why wooden doors stick in humidity!
Wood generates steam inside — Wrong. Water doesn't turn to steam at room temperature. Swelling happens because liquid water molecules are absorbed into wood's cellular structure.
Air pressure pushes wood out — Wrong. Air pressure doesn't push wood outward. Swelling is internal—water molecules entering and expanding the cellular structure of wood.