During research of the distribution of neutral hydrogen around various galactic objects it was revealed 11 rather exotic "envelopes", which were identified, as thin envelopes of neutral atomic gas around molecular clouds of middle density.
Their sizes are 80 X 300 pc, thickness is 15 pc, mean mass of neutral gas is 30000 mass of the Sun. The molecular clouds inside them have full density about 1000 cm(-3). With such characteristics these formations concern to a class of "superclouds".