McMaster-Carr 12" aluminum duct for toroid question

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

Original poster: "David Rieben" <drieben-at-midsouth.rr-dot-com> 

Hi all,

First let me thank you for your responses to my previous "large toroid
from innertube" thread. I think the choice for me has come down to one
of three types of 12" flexible aluminum duct hose from McMaster-Carr (thanks
"bunnykiller" Scot for your suggestion). I'm thinking of #1- part # 55335K49
- 21" compressed length to 72" fully extended length  with a 6" minimum
bend radius -- 4 or 5 pieces should be sufficient for a 12x48 toroid -- at
$22.30 each. Pros - relatively cheap and easily bendable. Cons - dents/crushes
easily. #2 - part #'s 5525K39 or 5525K49 which are Extendable aluminum
duct hose pieces that are supposed to each be 30" compressed length
and are extendable to 15 ft. ($47.97) and 30 ft. ($91.32), respectively,
with a bend radius of 7.2". Pros - more extendable and heavier thickness
than #55335K49 (.005" vs .004"), 12x48 toroid can be made w/ 2 of the 15 ft.
pieces, still fairly easily bendable w/ 7.2" bend radius. Cons - More cost-
ly than  #55335K49. And finally #3 - Semi-rigid aluminum duct hose
part#'s 5400K41 (5 ft. piece) or 5400K21 (10 ft. piece) with a cost of
$79.57 and $137.79, respectively, and has a bend radius of 12" .
Pros - very heavily built at .008" thickness for high crush and dent
resistance. Cons - quite costly and would still require at least 3 pieces
of the 5 ft length, shipping would be more expensive since it can't
be compressed to less than 5 ft. or 10 ft. long, and requires couplings
(part# 5518K21) -at- $17.59 each. BTW, they also offer the semi-ri-
gid duct hose in stainless steel but it's even more expensive than
the semi-rigid alum. duct and is very difficult to bend with a 24"
minimum bend radius, so that would pretty much be out
of the question for me.

So, my question is, which of these would make the best choice
for toroid construction on a budget? I'm thinking the Flex-lock
would work if  I got several pieces of it to minimize extention
of it and leave it as compressed as possible. This helps to main-
tain at least some degree of rigidity. I am concerned about
denting though as this stuff is pretty much ruined if it ever
gets a big dent in it. Some have mentioned spraying in that
expandable weatherizing urethane foam inside the toroid to
add some rigidity. Only problem is that stuff dosen't always
expand evenly and thus I'd probably end up w/ an ugly, lop-
sides toroid.   # 2 may also be workable since it's a little
heavier built and has more extendability to it, although it
is more costly.  Also, I'm not sure how the piece that's ex-
pandable to 30 ft. can have the same compressed length of
30" as the 15 ft. expandable stuff.  Maybe a typo on McM-
Carr's part?

I'm sorry for the long post but I would greatly appreciate
any comments/suggestions on this to help me make a
well-informed choice as to the toroid construction material.

Thanks,
David Rieben