[time-nuts] OXCO insulation

[Dave M]

What kind of foam insulation is generally used inside an OXCO?  Do all 
manufacturers use the same kind?  Is it available in small (hobbyist) 
amounts?

I've read that some folks have used Great Stuff polyurethane-based 
insulating foam to repair an OXCO.  I've used it to fill gaps around pipes 
in my home, but it's nor subjected to the high heat encountered in an OXCO. 
According to Dow's web site, it could present a fire hazard if subjected to 
temperature of 240F (115C).  There is a "Fireblock" variety, but it appears 
to have pretty much the same formulation as the other varieties, so I can't 
see any advantage to it.
Has anyone experienced any long term problems with Great Stuff in an OXCO?

Dave M