Abstract: Reduced boron containing glass fibers are provided which have a refractive index similar to that of higher boron-containing glass fiber compositions. The glass fibers with a refractive index in the range of greater than 1.5495 to around 1.57 have in weight percent SiO.sub.2 - 55-56.5, CaO - 20-23, Al.sub.2 O.sub.3 14.5-15.5, B.sub.2 O.sub.3 - 5 to 5.8, R.sub.2 O - 1-1.5, wherein R is an alkali metal and F.sub.2 - 0.4 to 0.6. In addition, the glass fiber composition can have minor constituents such as TiO.sub.2 of up to around 0.6 weight percent and an MgO of up to around 0.3 weight percent and ferric oxide of up to around 0.3 weight percent. Basically, the glass fibers have a reduced content of both B.sub.2 O.sub.3 and CaO over standard glass fiber compositions such as E-glass and 621-glass and also has elevated amounts of alkali and of refractory constituents such as SiO.sub.2 and Al.sub.2 O.sub.3. The glass fibers are formed with an elevated temperature of 40.degree. to 50.degree. F. (22.degree.-28.degree.

Abstract: Novel glass fibers are described which contain 58 to 60 percent SiO.sub.2, 11 to 13 percent Al.sub.2 O.sub.3, 21 to 23 percent CaO, 2 to 4 percent MgO and 1 to 5 percent TiO.sub.2. The fibers also have a seed count of 5 seeds or less per cc of glass and an electrical leakage value of 2.8 nanoamperes or less as measured by a test described in the specification.