Nice little rabbit hole for ya there

Huh, you yoy mention it

You're right, I meant "double glass" as the gas-filled thick panes typical for modern windows.

On a side note: I read that the isolation of gas-filled double glass actually degenerates over time. The vacuum does not.

It is as you suspected. The vacuum has very low conduction of heat and sound and is preserved by the small 'beads', if not, the two panes would simply be sucked onto each other. What do you mean by emissitvity?