The two types of glass we have standardized on is 6mm (1/4” thick) & 10mm (3/8” thick) The difference between the two types of glass is the STC rating associated with each thickness. The ¼”/6mm is rated around 31 STC and the 3/8”-10mm is rated around 34 STC. For smaller windows, a 6mm will suffice. Larger windows or projects with louder equipment can use a 10m or dual glaze