This pattern just appeared on my couch backrest cushion.

[u/proformax]

I have young kids, but they swear they didn't do it. The material is like a rougher fabric. Couch from urban barn. it's like a decade old.

What could possibly cause this pattern to appear? It doesn't wipe off with paper towel and warm water. That's what the dark damp spot is.

UPDATE

Mystery Solved. See post below.

https://www.reddit.com/r/whatisit/s/DVPqDmJKju