Yep – a warehouse ceiling for a cold-storage facility, photographed in the dark, with light spilling from another room, so the camera was also “fuzzy” due to the low light conditions :)

It’s mycelium. Mycelium on my ceiling. Mice-eating mycelium on my ceiling, to be exact. It’s horror beyond comprehension that’s also hard to say. It’s hard to say what it is exactly because exactly what it is is mice-eating mycelium on my ceiling.

Way too thin to add useful insulation. Much more likely for sound deadening to stop horrible echos.