Acquired 2 models for our entrance bedrooms as we've been on a loud principal road. Put in them yesterday and the real difference in noise is astounding. I went with the 6.4mm laminated glass and positioned the units on the entrance with the window sill to offer optimum hole. Secondary https://devinouafj.activablog.com/26572162/the-smart-trick-of-slimline-secondary-glazing-chelsea-that-no-one-is-discussing