A capsule for a heat-not-burn (HNB) aerosol-generating device may include a first frame, a second frame, a first heater, a second heater, and/or an aerosol-forming substrate. The first frame has a first interior face and a first exterior face. In addition, the first frame defines a first opening. The first heater may be secured to the first frame so as to cover the first opening. The second frame is connected to the first frame. The second frame has a second interior face and a second exterior face. Furthermore, the second frame defines a second opening. The second heater may be secured to the second frame so as to cover the second opening. The aerosol-forming substrate may be between the first heater and the second heater.