An aerosol delivery system comprising: an aerosol-generating device comprising: a device housing having an open-ended heating chamber configured to receive a carrier cartridge; a heater element disposed within the heating chamber and configured to receive at least a first end of a carrier cartridge, said heater element operable to heat a carrier substrate of a carrier unit of said carrier cartridge to cause release of an aerosol-forming precursor therefrom to generate an aerosol when gas is passed through the carrier cartridge; and a carrier cartridge comprising a carrier unit, said carrier unit comprising: a carrier substrate configured to hold an aerosol-forming precursor comprising a nicotine-containing and/or flavoured fluid, gel, wax, or powder; and a thermally conductive substrate configured to conduct heat from the heater element to the carrier substrate to cause release of said aerosol-forming precursor therefrom; and characterised in that: the thermally conductive substrate is formed into a cylinder and the carrier substrate is formed into an annular ring configured to fit around the thermally conductive substrate; and the thermally conductive substrate is formed from material that is penetrable by the heater element such that the thermally conductive substrate is penetrable by the heater element. an aerosol-generating device comprising: a device housing having an open-ended heating chamber configured to receive a carrier cartridge; a heater element disposed within the heating chamber and configured to receive at least a first end of a carrier cartridge, said heater element operable to heat a carrier substrate of a carrier unit of said carrier cartridge to cause release of an aerosol-forming precursor therefrom to generate an aerosol when gas is passed through the carrier cartridge; and a device housing having an open-ended heating chamber configured to receive a carrier cartridge; a heater element disposed within the heating chamber and configured to receive at least a first end of a carrier cartridge, said heater element operable to heat a carrier substrate of a carrier unit of said carrier cartridge to cause release of an aerosol-forming precursor therefrom to generate an aerosol when gas is passed through the carrier cartridge; and a carrier cartridge comprising a carrier unit, said carrier unit comprising: a carrier substrate configured to hold an aerosol-forming precursor comprising a nicotine-containing and/or flavoured fluid, gel, wax, or powder; and a thermally conductive substrate configured to conduct heat from the heater element to the carrier substrate to cause release of said aerosol-forming precursor therefrom; and characterised in that: the thermally conductive substrate is formed into a cylinder and the carrier substrate is formed into an annular ring configured to fit around the thermally conductive substrate; and the thermally conductive substrate is formed from material that is penetrable by the heater element such that the thermally conductive substrate is penetrable by the heater element. a carrier substrate configured to hold an aerosol-forming precursor comprising a nicotine-containing and/or flavoured fluid, gel, wax, or powder; and a thermally conductive substrate configured to conduct heat from the heater element to the carrier substrate to cause release of said aerosol-forming precursor therefrom; and characterised in that: the thermally conductive substrate is formed into a cylinder and the carrier substrate is formed into an annular ring configured to fit around the thermally conductive substrate; and the thermally conductive substrate is formed from material that is penetrable by the heater element such that the thermally conductive substrate is penetrable by the heater element. the thermally conductive substrate is formed into a cylinder and the carrier substrate is formed into an annular ring configured to fit around the thermally conductive substrate; and the thermally conductive substrate is formed from material that is penetrable by the heater element such that the thermally conductive substrate is penetrable by the heater element.