There are typically three panes of glass in a hurricane impact rated glass panel. We start with two layers of 6mm glass sandwiching a layer of .090 Polyvinyl Butyral, or PVB. This PVB interlayer is a strong binding resin and is used as a protective interlayer between the first and second 6mm pane of glass. The two panes and PVB interlayer between the glass provides the much needed hurricane resistance needed in Florida and coastal areas prone to hurricanes. Lastly, behind the two sandwiched layers of glass is a pocket of air about 6mm thick which is used as an insulator and then the last pane of 6mm glass. Altogether, the glass is 25mm thick (roughly 1 inch thick).