https://www.emergency.nsw.gov.au/Documents/factsheets/information-about-the-use-of-firefighting-retardants.pdf
What are they made of?
Long-term fire suppressants such as retardants are essentially fertilisers (ammonium and diammonium
sulphate and ammonium phosphate), with thickeners (guar gum) and corrosion inhibitors (for aircraft
safety).
Sometimes a red coloured pigment, made from iron oxide, is added so that those spraying can see where
they have released the fire retardant.
