Wash clothing and rinse as usual. If the clothing can't be washed, you can still spray the mixture on with a spray bottle.
Mix a batch of flame retardant in a large bucket. To one gallon of water, add about nine ounces of 20 Mule Team Borax and 4 ounces of boric acid.
Soak the clothing in the solution, or spray it on if the clothes can't be washed in water. Squeeze out the excess liquid and dry as usual.
Reapply the flame retardant mixture to the clothing after each washing or cleaning. It comes out in the wash.