Abstract: A curtain for defining a barrier in an underground passageway between a pair of spaced-apart pillars, comprising a bladder defined by a pair of flexible sheets joined together by a plurality of cords which define a cavity between the sheets and being open at a top edge thereof. The bladder is fastened to a ceiling of an underground passageway between a pair of spaced-apart pillars therein. A rigid foam is disposed within the cavity, being formed of a flowable hardenable material introduced into the cavity. A fire-retardant coating is applied to exposed surfaces of the bladder after the hardenable material has hardened. A method of closing gaps between pillars in mine galleries is disclosed.