Why does folding a piece of paper allow it to hold more weight?

Question

In this video: https://youtu.be/Ra_LM93R-Lk ,why does folding up the sides of the paper to make thicker walls on the bridge make the bridge so much stronger?

Answer 1

Because it increases the cross-sectional area of the edges. The total bending moment is now "distributed" across a wider cross-sectional area, leading to a lower strain.