<p>In recent years, the application of thin materials has witnessed a growing prevalence. Particularly, cotton cloth, which finds extensive utilization in clothing, curtains, and exterior wall decorative draperies, exhibits a propensity to rapidly develop into large-scale three-dimensional fires during the combustion process. Cotton cloth has been chosen as a representative material in this study; the effect of flame-retardant rates and coverage on the discrete flame spread over thin materials has been experimentally investigated. The experimental results revealed that the critical flame-retardant rate first increased and then decreased with the increase in coverage. Notably, when the coverage reached 60%, the discrete flame spread could be effectively inhibited. Additionally, with an increase in the flame-retardant rate, the duration of discrete flame spread is prolonged, while the mean flame length is reduced. The average flame standoff height and flame spread rate first increase and then decrease as coverage increases. The prediction models of the flame length and flame spread rate are established, and the relationship model between flame length and total heat release rate per unit width was further obtained. These findings provide valuable insights into the flammability characteristics of thin materials and their potential applications in fire safety.</p>