Multifunctional carboxylic acids have been used as durable press finishing agents for cotton with sodium hypophosphite (NaH2PO2) as the most effective catalyst. In our previous research, we found that cellulose cross-linking takes place when cotton fabric treated with a combination of maleic acid and NaH2PO2 is cured at 150 degrees C. The data suggested that H-P-H of hypophosphite likely reacts with > C=C < of the maleic acid already esterified with cotton cellulose, thus making it possible to form cross-linking on cotton. In this research, we studied the effect of the maleic acid (MA) and NaH2PO2 treatment on the fire performance of cotton using microscale combustion calorimetry. We found that esterification of cotton by MA reduces the flammability of the cotton cellulose. NaH2PO2 catalyzes the esterification of MA on cotton, thus further reducing the cotton fabric's flammability by increasing esterification on cotton. The quantity of ester formed on cotton reaches the optimum range when the curing temperature is increased to 140 degrees C. When the curing temperature reaches >= 150 degrees C, the reaction between NaH2PO2 and MA takes place on cotton. The bonding of hypophosphite to cotton further enhances the flame retardancy of the MA-treated cotton fabric as indicated by further decrease in heat release rate and further increase in char formation. The cotton fleece treated with the combination of maleic acid and NaH2PO2 at low concentrations is able to achieve class 1 flammability specified by 16 CFR 1610 at low concentrations.