Inner tubes

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Original poster: "Chris" <ct451-at-yahoo-dot-com> 

I've been trying to fill a 400x8 inner tube, the perfect size for my mini
coil, with construction foam without any success for a wile now and I was
wondering if anyone experimented with this idea.
The first time i tried just spraying some foam inside the tube and letting
it dry. This didn't work. The foam did solidify but when I removed the can
air trapped inside came out and the tube shrank.
Then i decided to puncture a bunch of holes all around another tube and
then fill it with the foam. This failed as well but got some pretty
sculptures from where the foam came out of the holes. Again the tube shrank
non-uniformly even though a lot of foam came out.
The foam does not set uniformly under pressure and the gasses separate and
escape.
For my next attempt I'm thinking of either keep shaking the tube so that
the gas is mixed with the foam until it solidifies or put the tube in an
airtight box and suck the air on the outside so that there's less pressure
inside the tube when the foam expands.
But perhaps there's a better approach or a different material I can fill
the tubes with.
The coil works fine for more than 45 mins on a run with an aluminium tray
as the top load but it would look so much better with a toroid.
These tubes cost about $1.50 each and the foam about  $4 for each attempt
so any help welcome,

Chris
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