After going through way too many backpacks that just end up falling apart, I bit the bullet and bought an Aer City Pack Pro and I couldn’t be happier. It’s rugged, durable, and most importantly: it stands upright on its own!!! Every other pack I’ve had just falls right over when setting it down. I also love that I can walk through pouring rain and none of my stuff gets wet.

I use a calculated sine wave to generate models of convoluted foam! (I’m a packaging engineer). And multivariable calculus can be used to predict cushion curves!