Acid corrosion and stress corrosion characteristics of E-glass fibers with and without boron (B2O3 or B) were carefully studied, using 1 N H2SO4 acid at 96 A degrees C and room temperature, respectively. The effect of boron on glass resistance to the acid attack is elucidated in conjunction with structural roles of B, Al, and Ca in the glass. Scanning electron microscopy with energy dispersive spectrometer (SEM/EDS) characterization was performed on the selective fiber samples before and after the acid leaching. For high boron-containing fibers, the results showed the formation of alteration layer enriched in Si as a result of depletion of both Ca and Al. Chemical analysis of the high boron fibers before and after 24 h acid leaching and the solution after 24 h test further confirmed that B, Ca, and Al in the glass fibers preferentially dissolved in the acid solution. Glass fiber dissolution mechanisms were discussed with a proposal that acid corrosion attack in boron-containing E-glass is controlled by hydrolysis of aluminoborate complex species (less than 10 nm) separated from the silicate glass network, whereas the acid corrosion attack in boron-free E-glass is controlled by hydrolysis of the silicate network, where 4-coordinated aluminum in the network is locally charge compensated by Ca.