PulmoGuard II Filter, Original Leader in PFT Filters. Transparent for easy, 100% visual inspection. Compact, non-intimidating design. Pleated media for better functionality. Features dead volume of less than 70mL. Meets ATS air resistance standards. Provides a cross-contamination efficiency of 99.999%. Safe, highly efficient and very affordable. Needs no adapter to fit many SDI spirometers. Fits many other PFT instruments with no adapter. Packaging: 50/Box.