Noted

https://www.cambridge.org/core/journals/mathematical-gazette/article/8055-a-maths-bite-how-to-impress-a-chemist/DC8DCAF9E9A76F4916097B0C38C9F0D5

The angle cos-1(-1/3) = 109.47°, familiar from soap films and tetrahedral molecular geometry, can be produced with an ordinary piece of A4 paper: Because it has a width:length ratio of 1:\sqrt{2}, folding it corner to corner as shown yields a shape with precisely that angle.

(Nick Lord, “A ‘Maths Bite’: How to Impress a Chemist,” Mathematical Gazette 80:489 [1996], 584-584.)