Same principle behind corrugated steel / I-Beams, C-Beams, cardboard. If you fold a piece of paper like an accordion, you'll find it's much harder to bend the

Same principle behind corrugated steel / I-Beams, C-Beams, cardboard. If you fold a piece of paper like an accordion, you'll find it's much harder to bend the paper along one axis but the parallel axis is easy. Notice the indentations on the jerrycan are in perpendicular directions (they look like an X).