Expanded hexagonal cores are commonly of Nomex and Korex aramid fiber construction.  Aramid fiber core has proven to have one of the highest strength to weight ratios in the business.  Cores of this type have been in use for over 50 years in aircraft and space applications.  The manufacturing  process of these cores consists of the aramid fiber sheets being bonded together to required cell size, the block is then expanded, reinforced with a high temperature phenolic resin, and sheared to required thickness.  This method allows the manufacturer the ability to give the consumer a wide range of core cell size, blanket size, thickness and density.  Although the optimum time to place perforations/vents within the core blanket is during manufacture, before expansion of the core, reinforcing (phenolic dip) the core after the block is expanded would seal any perforation/vent paths placed in the core, so consequently this technique does not allow for  perforation/venting to be placed within the cell wall during manufacture. 

Peterson Finishes, LLC provides the service of manually creating these perforation/vent holes.