Fire Retardant Sprays

I've found one.. Natfire.com. Couple of questions, One, does this stuff in any way close up the acoustic tranparency of burlap? Two, do I need anything better? Three, if I don't need a different brand, does anyone know if I should get the plain Flamex or the Flamex PF? thanks

Tommy, Rod answered this one and I caught your other identical post at RO - for others who may be interested, http://www.recording.org/ftopict-29704.html Steve