A cartridge for use in an aerosol-generating system is described. The cartridge comprises a liquid storage portion comprising a housing (24) for holding a liquid aerosol-forming substrate, wherein the liquid storage portion comprises at least two parts in fluid communication with each other. The first part (32) of the liquid storage portion comprises a heater assembly (46), a first capillary material (36), provided in contact with the heater assembly, and a second capillary material (38) in contact with the first capillary material and spaced apart from the heater assembly by the first capillary material. The the second part (34) of the liquid storage portion comprises a container for example a tank for holding aerosol-forming substrate in liquid form and supplying the liquid to the second capillary material.
