 The flame retardants work by coating the flammable fabrics with a mineral based barrier, preventing fire from reaching the fibres.Typically, the flame retardancy of topically treated fabric is certified for one year, though the actual length of time in which the treatment remains effective will vary based on the number of times the drapery is dry-cleaned and the environmental conditions in the location in which the drapery is used.It is recommended that topically treated drapery be re-tested for fire-retardancy on an annual basis and re-treated by a qualified professional as needed.