The Physical Test Methods Sub-Group had as objectives to collect available information about problems and concerns related to the pressure drop (PD) measurement of special filters and to conduct a study on the most common types of special filters.  A pre-study was conducted with a restricted number of participants to evaluate pressure drop mean values and variability for a set of selected special filter rods, compare results with existing data for mono-acetate filters and to prepare a technical report on the results which includes recommendations for a best practice of PD measurements of special filters.  The results of this pre-study are outlined in this report.