Spandrel glass is a heat processed glass with a ceramic frit permanently fused to the surface of the glass. Heat strengthening allows spandrel glass to be twice as strong as annealed glass. When tempered, spandrel glass is five times stronger than annealed glass and is more resistant to thermal stresses as well. Available in monolithic, laminated or insulating units, spandrel glass is widely used for building non-vision areas to mask construction materials. When used in curtain-wall systems along with vision glass, spandrel glass can help create the allusion that a building is constructed entirely of glass.