Bacteria impermeable, gas permeable package

Claim 1

In a package, which when sealed and sterilized in a sterilizing environment before or after sealing maintains the interior of said package in a bacteria-free condition after removal of said package from said sterilizing environment, said package comprising at least one unstretched microporous member which is impermeable to the passage of bacteria and which is permeable to the passage of gases between the exterior and interior of said package, the improvement wherein said microporous member comprises: (a) a matrix consisting essentially of essentially linear ultrahigh molecular weight polyolefin which is essentially linear ultrahigh molecular weight polyethylene having an intrinsic viscosity of at least about 18 deciliters/gram, essentially linear ultrahigh molecular weight polypropylene having an intrinsic viscosity of at least about 6 deciliters/gram, or a mixture thereof. (b) finely divided particulate substantially water-insoluble siliceous filler distributed throughout said matrix, said filler constituting from about 50 percent to about 90 percent by weight of said microporous member, and (c) a network of interconnecting pores communicating throughout said microporous member, said pores constituting from about 35 to about 80 percent by volume of said microporous member.