The description hints that this coat may melt if exposed to fire. I notice there's a gap in the Items by ID right after it (the coat is #838, and there's a gap at 840). Maybe if you take enough damage from a fire attack it will melt and yield a new material? I'm trying to test this, but it's hard to find opponents who use fire attacks outside of PvP.
EDIT: I had no luck getting hit by microrocket, even with tamed fire equipped to lower my fire defense. Crypto tried the scalding steam and getting hit by nitro technique to no avail. Maybe jumping into the Lake of Fire would do the trick?