There is provided a heat source for a smoking article, including an upstream end and an opposed downstream end, and further including a combustible carbonaceous core and an integral, non-combustible, thermally insulating, peripheral layer. The core extends from the upstream end of the heat source the downstream end of the heat source. The peripheral layer extends from the upstream end of the heat source only part way along the length of the heat source and circumscribes an upstream portion of the core.