A capsule for a heat-not-burn (HNB) aerosol-generating device may include a base of a thermally-conductive material, the base defining a first cavity therein, the base including a first surface, the first surface defining an opening to a second cavity, the first surface including a first plurality of apertures through the first surface. The capsule may further include a cover coupled to the base and on the base, the cover including a second plurality of apertures in a middle portion of the cover, the first plurality of apertures and the second plurality of apertures defining an air flow path through the base and the cover.