It's solid fiberglass blocks cut into shape covered by a fiberglass cloth covered by a stainless wire mesh that's grounded to reduce RFI.
The "floor" is a tensioned wire grid with the same acoustical blocks below it. It's kinda bouncy.
The teeny-tiny mic on the stand is about 35 grand-it has ultra low noise floor electronics.
At most, the space is 12 feet wide.