A new method of measuring the acoustic parameters of porous materials is described. The method is based on the measurement of radiation impedance at the end of an open flanged pipe placed against a sample. Five samples of polystyrene foam of differing porosities have been used to assess the usefulness of the method. The acoustic characteristics of the samples were first determined using a conventional acoustic impedance tube with rigid end cap. Estimates of the acoustic parameters of the samples—sound speed and attenuation constant—were then obtained by applying various acoustic models to match the measured characteristics. Open tube measurements were then made on the samples and these impedance characteristics compared with those predicted by application of acoustic models. Moderately good agreement was obtained between measured and predicted impedance although the values of acoustic parameters derived deviated from those obtained from the closed tube measurements. The results confirm the potential of the method to be developed into an alternative method of measurement of acoustic absorptivity.