Unbleached (gray) cotton needle-punched nonwoven (NW) fabrics with 12.5% polypropylene scrim were treated with two phosphate–nitrogen-based flame retardant (FR) formulations, Southern Regional Research Center (SRRC)-1 and SRRC-2. The SRRC-1 formulation contains diammonium phosphate as the FR chemical along with urea and dimethyloldihydroxyethyleneurea. Because a trace amount of formaldehyde was still expected to be released from SRRC-1-treated FR cotton under high heat, it was preferable to eliminate the dimethyloldihydroxyethyleneurea, leading to the revised formulation SRRC-2. It has a higher content of diammonium phosphate and did not use the polyethylene emulsion that was in SRRC-1. Both formulations were of low cost as they were developed at SRRC using industrial grade chemicals. The fabrics were evaluated with a cone calorimeter using three heat flux levels, 20, 30, and 50 kW/m2. On the basis of the overall cone calorimeter results for heat released and ignition times, FR NW fabrics that were treated with SRRC-2 were found to be slightly superior in flammability properties to those treated with the earlier SRRC-1 formulation, but the differences were statistically insignificant. Both preparations were much less flammable than the untreated control cotton NW fabrics. Compared with the untreated NW fabrics, the FR fabrics had higher visible smoke production. Copyright © 2012 John Wiley & Sons, Ltd.