For people who have done this before:

1. About how many cans do you need to fill the average bathtub?

2. Whats cleanup like? Obviously the stuff washes away with water, but are there special considerations at that volume?

I'd be more concerned about the large amount of fumes...

I just stood 8 cans at a time in the bottom of the bath and used a tea tray to press down on them simultaneously - I have filled a uk size bath tub to the top before, which overflowed when I got in,. it took about 30 400ml sized cans = cheap erasmic foam I believe

For my tub it takes 50 cans at 11 ounces each (or roughly 325ml) to fill a tub enough to submerge in. Check out my pics if you want to see for yourself!

The most I have used was 8 regular sized cans. I was underwhelmed at the results. I should have used at least triple.