A fill pack includes a first sheet and a second sheet. The first sheet has a first end, a second end and a first plurality of flutes. A first microstructure includes first top flat strips, first bottom flat strips and first conduit sides connecting the first top flat strips to the first bottom flat strips. A plurality of first radii connect the first top flat strips to the first conduit sides and the first bottom flat strips to the first conduit sides. The second sheet has a second plurality of flutes. A second microstructure includes second top flat strips, second bottom flat strips and second conduit sides connecting the second top flat strips to the second bottom flat strips. A plurality of second radii connect the second top flat strips to the second conduit sides and second bottom flat strips to the second conduit sides.