DFR = Durably Flame Retardant
In earlier days, the only fabrics that were flame resistant for a lifetime were IFR fabrics sewn with fibers derived from asbestos and fiberglass. Over time, manufacturers and chemists developed textiles from polymer extruded filament fibers (nylon and polyester), along with additives that chemically bind to the fibers that provide flame resistance and do not react to water. It essentially renders these fabrics flame resistant for a lifetime.
While there are chemical solvents that can alter the flame resistant properties of these fabrics, such chemicals are not usually encountered when fabrics are used as draperies or decorations. Since these treated fabrics will remain fire resistant for a lifetime under normal circumstances, the industry labels them “durably flame retardant.”