I have been watching some of the debate about how Acetone is "Bad" for PEI surfaces... I find it highly amusing to observe many of these "armchair engineers & chemists" making declarations about how Acetone will ruin PEI (or Polyetherimide) sheets if you wipe your print surface with it... so I figured I would lay the debate to rest with some facts... As you can see from this quickly searched chemical resistance chart I found with a simple search, polyetherimide has great chemical resistance to acetone... The best place to get your facts is from the source itself. One caveat I will mention, acetone *is* flammable and it is a *really* bad idea to try to wipe down a hot print bed or heat one up immediately after cleaning with acetone. Make sure the print bed is fully cooled to prevent excessive vapors and possible ignition.