What causes Bakelite to harden?

Bakelite hardens through a process called polymerization, specifically condensation polymerization. This occurs when phenol and formaldehyde react under heat and pressure, forming long chains of interconnected molecules. As the reaction proceeds, the material transitions from a liquid to a solid state, creating a rigid, thermosetting plastic that cannot be re-molded once cured. The cross-linking of polymer chains contributes to Bakelite's durability and heat resistance.