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Phenol-formaldehyde resins, also known as PF resins, are synthetic polymers produced by condensation of phenol with formaldehyde. They are thermosetting polymers that form crosslinked networks upon curing and do not melt or flow after hardening.

First developed by Leo Baekeland in 1909, PF resins gained early fame as Bakelite, the first commercially produced synthetic plastic. They found widespread use in electrical insulators, radio housings, and a variety of molded parts due to their high heat resistance and electrical insulating properties.

There are two main families: novolacs and resols. Novolac resins are produced under acid catalysis with a phenol-to-formaldehyde ratio that yields linear oligomers; they require additional curing agents, such as hexamethylenetetramine, to form a rigid network. Resol resins are formed with excess formaldehyde under basic conditions and can cure autonomously upon heating. The resin type, formaldehyde content, and catalysts determine processing and final properties.

Properties include high thermal stability, flame resistance, and good dimensional stability; excellent electrical insulation; but brittleness and relatively low impact strength when cured; resistance to water and many solvents varies with formulation.

Applications include laminates, coatings, adhesives, and molded parts for electrical and automotive components; high-pressure laminates and phenolic resins are used in specialized electrical insulators, industrial panels, and cabinetry.

Safety and environmental: formaldehyde and phenol are hazardous during production and handling; emissions controls are important. Once cured, PF resins are relatively inert, but uncured resins require ventilation and protective equipment.