Wiktionary
filling gas
n. Any nonreactive gas that is used to fill containers of perishable produce, tyres etc
Usage examples of "filling gas".
She eyed the slowly filling gas bag and wished again they could have transported in enough helium to do the job, but wishing was pointless.
It took fifteen or twenty minutes for the filling gas bags to lift the cabin clear of the sea.
It was the end of a Saturday serial that leaves the hero locked in a slowly filling gas chamber.