Cotton fabrics flame retarded with tetrakis (hydroxymethyl phosphonium chloride (THPC)-urea-ammonia polycondensate (Proban CC, Albright and Wilson Ltd., U.K.) have been subjected to up to 50 simulated hospital wash cycles. Laundering variables include sodium perborate oxidant concentration, detergent type (liquid with no oxidant, powder with zeolite and sodium perborate and powder with polyphosphate and carbonate and perborate) and water hardness. The flame retardant system resisted all laundering systems in terms of the constancy of burning behaviour assessed by vertical strip (BS 5438) and *Edator's Note: A reviewer of this paper has pointed out that the authors' use of the terms &dquo;flame retardant&dquo; and &dquo;flame resistant&dquo; is not in accord with practice now generally followed in the U.S. Since the Journal is international in its circulation, we hesitate to require conformation to U.S. practice except in the interest of avoiding confusion for readers. The terms as used here should not cause such a problem. Downloaded from 336 limiting oxygen index (LOI) measurements. However, increased perborate concentration changed the thermogravimetric (TGA) response of laundered fabrics.Soft water washing promoted cotton fibre fibrillation independent of detergent type; increased oxidant concentration promoted secondary wall damage. Hard water washing severely damaged fibre secondary walls and significant depositions of calcium ions often as phosphate occurred on fabric. Presence of the flame retardant was observed to have a stabilising fibrillar binding effect which was offset by a secondary wall crack promoting character.