Because the bed is heated from the bottom, heats the air, which then floats to the sides off, so the bed can reheat the cold air again. As I said: For me adding the bed halved the heating time.
Yeah, it is a foam board, with adhesive on one side and aluminum foil on the other.
You use scissors cut out, where e.g. the LEDs or the bed clamps take space underneath, remove the protective film and press it on.
Here is the one i have on order.
I guess you got the last 1. Apparently, it’s now unavailable. 
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Weird i just clicked on the item again and it shows in stock. Maybe they just don’t like you ?
Story of my life… ?
From what I heard the same stuff is used to insulate exhausts of motor cycles, so you may get them in bike/car stores locally.
I guess this is just an overpriced cutout from the original. Or you only get 3x0.50m rolls for 40 Euro, which is cheap, but also way to much. 
Like the belt printer belt is just a luggage conveyor belt.
Found it:
Some of them for sure, although I have seen PEI coated belts… an interesting option.
Yea i could have paid 8 dollars more for a lot more, but i would never use it. So paying 8 dollars more for something i would never use to me is just a waste of money. Of course i could not get it at all and save 10.99 but where is the fun in that ?
Well, I´ll need a 400x400 sheet to get most off my 750W heat bed, once the GeitPrinter is up and running.
