NOVELTY - A composition (C1) for preparing high strength glass fibers comprises (wt.% of the total composition): silicon dioxide (SiO2) (70.6-79.6); aluminum oxide (Al2O3) (10.0-18.5); magnesium oxide (MgO) (10.0-19.0); calcium oxide (CaO) (0.1-5.0); lithium oxide (Li2O) (0-3.0); and sodium oxide (Na2O) (0-3.0).    USE - As composition for preparing high strength and high performance glass fibers; for forming reinforced composite product in the form of wind blade (claimed) and in aerospace structures.    ADVANTAGE - The composition is free of B2O3 and fluorine. The composition has a Delta T up to about 139 or 210 degrees C and has a log 3 temperature of less than about 1525 or 1530 degrees C or 1268-1525 or 1530 degrees C and has a liquidus temperature no greater than about 1470 degrees C. The glass fiber has a specific modulus of 3.40x 107-3.6x 107 (preferably 3.40x 107-3.56x 107) J/kg and a specific strength of 1.7x 106-2.0 or 2.14x 106 (preferably 1.85x 106-2.14x 106) J/kg. The glass fiber has a pristine fiber tensile strength of 4150-4960 or 5233 (preferably 4590-5230) MPa, a modulus of 80-88 (preferably 82.8-87.4) GPa and density of 2.37-2.51 (preferably 2.39-2.48) g/cc. The glass fiber is high strength glass fiber. The glass fibers formed from the composition possess exceptionally high modulus and a low density, which make them particularly suitable in applications that require high strength, high stiffness and low weight such as wind blades and aerospace structures. The composition retains favorable mechanical and physical properties such as specific modulus and tensile strength and forming properties such as liquidus temperature and forming temperature, where the forming temperature is low and the difference between the forming and liquidus temperatures is large enough to enable the components of the glass composition to be melted in a conventional refractory tank. The fibers are formed at lower cost due to the lower energy input needed to melt the glass composition. The composition utilizes low cost refractory melters instead of conventional high cost platinum-alloy lined melters in the formation of the glass fibers.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a high strength glass fiber produced from the composition (C1);    (2) a method of forming high performance glass fiber involving: providing a molten glass composition including the composition (C1); and drawing the molten glass composition through orifices in a bushing to form a continuous glass fiber; and    (3) a reinforced composite product comprising a polymer matrix; and several glass fibers, where the glass fibers are produced from the composition (C1).