A heat-not-burn tobacco aerosol source member or consumable includes a first heating section with a front end. The first heating section contains a liquid aerosol precursor existing as a free liquid in an unbound form. A second heating section is provided with a mouth end. The second heating section contains a solid tobacco substrate. A first thermal barrier that is vapor permeable but liquid impermeable is located between the first heating section and the second heating section. The system has a simple structure and lowers processing costs, and greatly reduces undesirable harmful chemicals because of its lower heating temperatures for the first and second heating sections of the consumable.