Oops quite a bit of confusion going around.
Andy Peters:
ESR is the real cause of heating
www.dearborncaps.com/tech_papers/ppc_6.htm

In the earlier days there were electrolytic caps in the axial package, in which the can was usually the negative terminal. So for electrical safety it was necessary to have that electrically insulating sleeve. With most materials electrically insulating is also thermally insulating and this sleeve is no longer necessary with the radial caps, with electrically isolated can. On no other electronic component do we deliberately put insulating material when we know there will be some temperature rise, more so on a component considered to be of relatively short life. So considering extreme compactness we are trying to achieve in our products, may be elimination of this sleeve will add that minor improvement to capacitor life.
No I do not allow caps to heat up to 85C but in most electrolytic cap circuits there will be significant heating because in most circuits the purpose of electrolytic caps is ripple filtering, which is why the manufacturer specifies the ESR and the ripple current rating.