A fill pack for use with a heat exchange apparatus having a first axis and a second axis, comprising: a plurality of sheets (12, 14), each sheet having first, second, third and fourth edges, wherein each sheet (12, 14) generally lies in a plane that is generally parallel to the first axis and said plurality of sheets (12, 14) combine to form a plurality of first conduits and a plurality of second conduits, each sheet (12, 14) further comprising: a first vertical rib that extends in a first direction generally parallel to the first axis along the sheet (12, 14), substantially all the way between the first and second edges, wherein said first vertical rib protrudes in a second direction out of the plane; a second vertical rib that extends in the first direction along the sheet (12, 14), substantially all the way between the first and second edges generally parallel to said first vertical rib, wherein said second vertical rib protrudes in the second direction out of the plane; a first horizontal rib that extends in a third direction generally parallel to the second axis along the sheet substantially all the way between the third and fourth edges, wherein said first horizontal rib protrudes in a fourth direction opposite said second direction, into the plane, wherein said first horizontal rib intersects said first vertical rib; a second horizontal rib that extends in the third direction along the sheet (12, 14) substantially all the way between the third and fourth edges generally parallel to said first horizontal rib, wherein said second horizontal rib protrudes in the fourth direction opposite said second direction, into the plane, wherein said second horizontal rib intersects said second vertical rib, wherein said first and second vertical ribs and said first and second horizontal ribs form a boundary that surrounds at least one generally planar region; at least one stiffened corner, wherein said at least one stiffened corner (52, 54) includes said plurality of first and second conduits (16, 18) wherein adjacent ones of said plurality of conduits (16, 18) contact one another and wherein said first edge and said third edge are load bearing at said at least one stiffened corner; wherein said adjacent conduits (16, 18) that contact one another combine to form a honeycomb geometry; wherein said honeycomb geometry of each stiffened corner of each sheet (12, 14) is positioned so that the honeycomb geometries of adjacent sheets (12, 14) contact each other along a full face of adjacent honeycomb cells; characterized in that adjacent sheets (12, 14) mirror one another. a first vertical rib that extends in a first direction generally parallel to the first axis along the sheet (12, 14), substantially all the way between the first and second edges, wherein said first vertical rib protrudes in a second direction out of the plane; a second vertical rib that extends in the first direction along the sheet (12, 14), substantially all the way between the first and second edges generally parallel to said first vertical rib, wherein said second vertical rib protrudes in the second direction out of the plane; a first horizontal rib that extends in a third direction generally parallel to the second axis along the sheet substantially all the way between the third and fourth edges, wherein said first horizontal rib protrudes in a fourth direction opposite said second direction, into the plane, wherein said first horizontal rib intersects said first vertical rib; a second horizontal rib that extends in the third direction along the sheet (12, 14) substantially all the way between the third and fourth edges generally parallel to said first horizontal rib, wherein said second horizontal rib protrudes in the fourth direction opposite said second direction, into the plane, wherein said second horizontal rib intersects said second vertical rib, wherein said first and second vertical ribs and said first and second horizontal ribs form a boundary that surrounds at least one generally planar region; at least one stiffened corner, wherein said at least one stiffened corner (52, 54) includes said plurality of first and second conduits (16, 18) wherein adjacent ones of said plurality of conduits (16, 18) contact one another and wherein said first edge and said third edge are load bearing at said at least one stiffened corner; wherein said adjacent conduits (16, 18) that contact one another combine to form a honeycomb geometry; wherein said honeycomb geometry of each stiffened corner of each sheet (12, 14) is positioned so that the honeycomb geometries of adjacent sheets (12, 14) contact each other along a full face of adjacent honeycomb cells; characterized in that adjacent sheets (12, 14) mirror one another.