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Phenol formaldehyde resins, also known as phenolic resins or Bakelite, are synthetic polymers formed from the reaction of phenol with formaldehyde. This reaction, often carried out in the presence of an acid or base catalyst, results in a thermosetting plastic. There are two main types of phenol formaldehyde resins: resole resins and novolac resins, differing in their molar ratio of phenol to formaldehyde and the curing mechanism. Resole resins are produced with an excess of formaldehyde and can be cured with heat alone, while novolac resins are produced with an excess of phenol and require a curing agent, typically hexamethylenetetramine, to crosslink.

These resins are characterized by their excellent thermal stability, chemical resistance, and electrical insulating properties. They are rigid and brittle in their cured state but can be processed in a liquid or malleable form before curing. Applications for phenol formaldehyde resins are diverse and include their use as adhesives for plywood and laminates, binders for abrasive materials like grinding wheels, molding compounds for electrical components and automotive parts, and as coatings and impregnating agents. Their historical significance is notable as Bakelite was one of the first synthetic plastics to be produced commercially, revolutionizing manufacturing and consumer goods. Despite the development of newer polymers, phenol formaldehyde resins remain important in specialized industrial applications due to their cost-effectiveness and robust performance characteristics.