After the Great Depression and the subsequent technology boom in the 20th century
, the process of manufacturing laminated glass evolved considerably. While the initial material for glass lamination was cellulose, today it is a chemical substance called polyvinyl butyral (or PVB) that is used as a substrate between two sheets of glass. Unlike old cellulose, which tended to darken over time, modern laminated glass remains transparent regardless of its exposure to the sun. Another benefit of laminated glass is its sound-proofing qualities. Laminated glass also prevents ultraviolet light from penetrating the windshield and damaging the interior of the car (as well as the driver's skin!). It is said that at least 95% of the sun's harmful ultraviolet rays are effectively blocked by a laminated windshield.