PU and EPS boards both get hot in the sun. Why do EPS boards *need* vents? More air volume? resin bonding to substrate in a EPS/Epoxy combo not as robust as with PU/PE or PU/Epoxy?
If any water gets in the board, EPS foam has air pockets inside that heat up into steam and push on the glass, delaminating it. The vents prevent that.
PU has no air and no steam but delaminates from the foam crushing and breaking away from the glass.
EPS / epoxy construction is 5X stronger than PU with the same glass schedule.