PURPOSE: To obtain a hydrophobia glass fiber insulating material by deposting a hydrophobic resin compsn. consisting of thermosetting resin precursor aq. soln., metal soap, and surfactant on glass fiber and subjecting the glass fiber to heat treatment at specified temp.

CONSTITUTION: The hydrophobic resin compsn. is prepared by mixing 1-70wt.% (calculated as a resin precursor) of a resin precursor aq. soln. or water-base emulsion of thermosetting resin such as phenol resin, water-dispersion liquid containing 0.1-20wt.% metal soap comprising long-chain fatty acid salt of 12-24C such as zinc stearate, 0.05-10wt.% surfactant such as anion surfactant, and water in a homomixer or the like for 5-60 minutes. Then the obtd. compsn. is deposited on the surface of glass fiber by spraying, etc., and heated at 150-200°C which is higher than the melting point of metal soap and lower than the hardening temp. of the thermosetting resin. Thus, the hydrophobic glass fiber insulating material is obtd.