I *think* I remember seeing something in the way of a fire retardant for cloth - not sure where now, of course as it's been a while. It was a powder you mixed with water, then soaked the item in until thoroughly wet, then let air dry IIRC. A search might turn something up?
Loving fantasy since 1960 or so, FRPGs since 1975 (appx), and CRPGs since 1985....
When the Dark comes rising, six shall turn it back,
Three from the Circle, three from the track;
Wood, bronze, iron; water, fire, stone:
Five will return, and one go on alone.