Patent ID: 7449243

Claim:
Reinforcing glass yarn, the composition of which comprises the following constituents, within the limits defined below, expressed in percentages by weight: SiO 2 54.5 to 58% Al 2 O 3 12 to 15.5% SiO 2 + Al 2 O 3 70 to 73% CaO 17 to 25% MgO 0 to 5% RO = CaO + MgO 21 to 28% R 2 O = Na 2 O + K 2 O + Li 2 O up to 2% TiO 2 less than 1% Fe 2 O 3 less than 0.5% B 2 O 3 up to 3% F 2 less than 1% and such that the ratio R 1 =Al 2 O 3 /CaO is less than 0.7, and when SiO 2 is greater than 57% the amount of boron oxide B 2 O 3 is greater than 2%, wherein the composition further satisfies the criterion: 2.35<R 2 =(SiO 2 +Al 2 O 3 )/(RO+R 2 O+B 2 O 3 )<2.70, a T (log 2.5) of at least 1300° C., its liquidus temperature is less than or equal to 1200° C., and its fiberizing temperature range is greater than 100° C.