Dryer duct toroid?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Black Moon" <black_moons-at-hotmail-dot-com> 

Hi, Iv heard of making a toroid with that flexable plastic dryer exhaust 
duct, about 4" across, has a metal 'spring' that keeps it from collapseing.
Now, Iv found some duct laying around my house (Not even attached to a 
dryer, bonus at not having to disassemble the house!) but it kinda shrinks 
into a little stack, and when I make a loop out of it, its like 3" inside 
diamiter... so im kinda wondering, what do I do to make it rigid in the 
large toroid shape? are there any websites detailing making one?