Bought 2 units for our front bedrooms as we've been on a loud key street. Put in them yesterday and the real difference in noise is wonderful. I went for that 6.4mm laminated glass and positioned the units within the front in the window sill to give highest gap. Lastly, https://alcuinj543vjx8.theblogfairy.com/26597210/rumored-buzz-on-energy-efficient-glazing-in-sw3