A retrofit cover for fully or partially enclosing a mattress, wherein the cover is formed of a unitary, integrally formed fabric having a fire barrier element. The cover is capable of rendering mattresses, mattress foundations, upholstered furniture article and other articles filled with resilient cushioning materials that were not originally manufactured to meet a full-scale open flame standard capable of passing such newly mandated standard for performance in newly manufactured items. When tested in accordance with the flame resistance test protocols of 16 CFR 1633 or TB 603, the item encased in the retrofit cover has a maximum heat release rate of less than 200 kW and a total energy release of less than 25 MJ in the first five minutes of the test.