Cellulose Insulation

The use of borates in cellulose insulation greatly increases the fire
retardancy of the product.  Because borates are incombustible and will melt
and release water in a fire situation, they are inherently excellent fire
retardants.  Boric Acid is an excellent after-glow suppressant that will
quickly extinguish an ignition source by releasing water.  Borax 5 Mol forms
a thermal barrier inhibiting the spread of flames by fusing into a glass
matrix during combustion by melting.