The thermal degradation of wool treated with the flame retardant synergistic system, zirconium acetate, acid citric, and hydrochloric acid, was studied by thermal analysis, mass loss, the limiting oxygen index (LOI), and the vertical flame test. SEM pictures were provided to study the morphology of the treated samples. The flame-retardant treated wool indicated a decrease in the temperature of decomposition, an increase in the residual mass and LOI, comparing with the untreated wool. The central composite design (CCD) was used for the experimental plan with four variables on the results of flame retardant. Statistical analysis confirmed the optimum conditions obtained by the experimental results. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012