Expanded hexagonal and flexible core are used in the manufacture of aerospace hardware.  This hardware includes, but is not limited to, satellite bodies, solar substrate panels, solar cell assemblies and satellite reflectors.  These types of space hardware are typically manufactured with sandwich construction.   This is a design in which the core blanket is bonded between two face sheets. These face sheets are usually composed of a composite or aluminum material.  The hardware is assembled on earth with one atmosphere of pressure, 14.7 PSI.  When launched into space, within 90 seconds the hardware is in a complete vacuum.  If there were no path for the air to escape from a sandwich type panel, it would remain pressurized and would try to break it's own bonds.  The core blanket is the means of allowing pressure to escape.  So the expanded core cells, which can typically be as small as an eighth of an inch in diameter, each need a hole approximately .030" in diameter to allow the atmosphere to escape.  The manual process which creates the vent path is called perforation or venting.