Well, if we’re ruling out PET and PETG – PET would probably require the temperatures you describe and would be impervious to acetone, as well as extremely flexible – there is an outside possibility it could be HDPE.

HDPE filament is damn rare, though, and I’d doubt anyone would be giving it away as samples given how difficult it’d be to print with most consumer machines. HDPE’s signature tell is that it feels somewhat waxy if you e.g. scrape at it with your fingernail.