The owners manual for cloth shake-out bag equipped machines recommended that the bag be emptied after cleaning had been finished, to avoid dirt, fungus and bacteria from setting deep in the fibers of the bag, and preparing the machine for the next time. The cloth bag can be laundered periodically, if necessary. Starting with the Tradition model, an internal, disposable paper bag was introduced optionally in addition to the cloth shake-out bag, so that customers could decide which method they preferred. The disposable paper bag provided a protective barrier against the interior surface of the cloth bag, and offered the convenience of storing the cleaner when finished, not requiring that the bag be emptied every time. The disposable paper bags became standard following the release of the Heritage model, with the shake-out bag becoming optional. Starting in 1984 with the Heritage II, the "Sani-Emtor" became the "Mini-Emtor", which no longer had a removable lid on the bottom, but still trapped larger, heavier objects. The introduction of the Generation 3 in 1990 marked the end of the shake-out bag, with disposable paper bags being the only method of dirt containment. In 1993, with the introduction of the G4, the disposable paper bag filtration was improved, labeled "Micron Magic", and was capable of trapping down to three microns, while the outer cloth bag trapped any remaining particles that pass through. Starting with the Gsix in 1999, H10 HEPA multi layered paper bags were introduced, then in early 2003 the revised version of the Ultimate G introduced as the Ultimate G Diamond Edition, the disposable paper bag was upgraded once more to H11 HEPA standards. Starting with the Sentria in 2006, Kirby bags are no longer made of paper, but polypropylene, a cloth-like fabric.