Abstract: This invention relates to improved sheets of flash-spun plexifilamentary film-fibrils useful in fluid microfiltration and sterile packaging. The sheet material suitable for use in microfiltration of liquids has a permeability that causes a pressure drop of less than 21 kPa at a water flow rate per unit area of 12.55 ml/min/cm.sup.2, and that has a filtration efficiency of 99% of dust particulates in the size range of 1 to 2 microns suspended in a stream of distilled water pumped through the sheet material at a pressure differential of 207 kPa. The sheet material suitable for use in sterile packaging that has a Gurley Hill Porosity of less than 15 seconds and a bacteria spore log reduction value of at least 2.5.