This study presents the improvement of durable flame retardant (FR) effect of 100 % cotton fabrics via chemical foaming system which provides energy and water saving significantly, compared to conventional methods. In order to carry out the experiments, dialkylphosphonocarboxylic acid amide based flame retardant agent and auxiliary chemicals were applied on cotton fabrics in a foam formed. Foam parameters such as blow ratios and wet-pick-up ratios were varied and flame retardant properties of foamed cotton fabrics were compared with cotton fabrics treated through pad-dry-cure process in order to determine the performance effect of cotton fabrics in flame retardancy via different finishing methods. After the finishing processes, flame retardant effect of all treated fabrics was examined with vertical burning test method. As durability of flame retardant applied cotton fabrics against washing process is one of the most important subjects that has been tried to be improved with different approaches for a long time, all treated fabrics were washed and dried 50 times, separately. After repeated washing and drying cycles, burning behavior of washed and FR treated fabrics were also tested vertically for determining flame retardancy effect. Beside the vertical burning test, tearing strength test, color spectrums, SEM and SEM-EDX analysis of fabrics were carried out. According to test results, even at the low wet-pick-up ratios, a significant increase was observed in flame retardant effect of cotton fabrics that were treated with FR agents via foam application. Moreover, all treated fabrics were durable against 50 washing and 50 drying processes.