Used as a flame retardant additive in polymers, particularly in engineering plastics such as polyamides and polyesters. It functions as an organophosphorus compound that promotes char formation during combustion, reducing flammability and suppressing smoke generation. Commonly applied in electronics, automotive components, and textiles where thermal stability and fire safety are critical. It is especially effective in halogen-free flame retardant systems, making it suitable for environmentally regulated applications.