Disclosed is a carton having adjustable air passages and a blank for forming it. The carton is formed of slidable inner and outer tapered sleeves having complementary spaced openings. The openings are positioned to provide open air passages when the inner sleeve is slid to a first position, and to close the passages as the inner sleeve is moved toward a second position. A stop is provided in the outer sleeve to limit movement of the inner sleeve when slid to the first position, while the taper between the sleeves precludes undue movement of the sleeves past the second position. A shiftable tab is also provided on the outer sleeve to block sliding movement of the sleeves relative to each other until the carton is ready for initial use.