The characteristics of acoustic linings, which employ felt-type material made of polymidefamily fiber, has been studied by the authors. This material is considered to be one of the future candidates which take the place of HELMHOLTS-resonator-type lining which is commonly used today. To accomplish this purpose, measurement of acoustic characteristics including acoustic impedance as well as sound absorptionwas carried out systematically. In conjunction with the measurement, the procedure to calculate those acoustic characteristics of linings of this kind has been developed. Through these studies, it is shown that polymide-family felt has a superior property as acoustic linings. Agreement between measurement and calculation was good. The calculation method is considered to be a useful tool to find lining dimensions which give us desired characteristics.