I noticed while staying at the Radisson SAS at Stansted airport
recently that even though the whole of one wall is made of glass that
you cannot hear *anything* from outside. No aircraft despite being
only a few hundred metres from the runway, no traffic and no
roadworks.

The glass is a little dark, but seems to be totally soundproof. I
wouldn't mind glass like this on our bedroom window since I am a light
sleeper and just about anything from birds to motorbikes on the road
200m away wake me up.

How soundproof can you make glass and how is it done? I guess it would
be extremely expensive?