香烟燃烧后生成的炭
参见下文：The Cigarette Extinction Method uses a set number of layers of standard filter paperd as a heat-absorbing substrate.The filter paper acts as a heat sink for the burning cigarette and once the cigarette coal has cooled to a certain temperature it should self-extinguish.
不是中国英语,网页上有非常多资料显示这个词组