A heater assembly for an aerosol-generating system is provided, including: a fluid-permeable heating element to vaporise a liquid aerosol-forming substrate; and a transport material to transport the substrate to the heating element and having a thickness defined between a first surface and an opposing second surface thereof, the first surface being in fluid communication with the element and the second surface being arranged to receive the substrate and provided with at least one hole extending into the material to a depth corresponding to at least a part of the thickness to define a formed fluid channel for the substrate, the material including a capillary material having elongate fibres, an average direction of the fibres is substantially parallel to the first and second surfaces, and the hole extends substantially perpendicular to the average direction. A method of manufacturing a heater assembly, a cartridge, and an aerosol-generating system are also provided.