STC thirty–35 = This is an elevated degree of sound abatement efficiency. You could possibly hear a loud, outdoor dialogue but wouldn’t be able to make out the text. Perspex or plastic is cheaper and will do a similar job, but will discolour with age; it is more generally used https://shirinj135opn8.blogtov.com/6835562/the-ultimate-guide-to-condensation-resistant-glazing-in-wc1a