Limiting and extinction oxygen index techniques have been used to study the effects that fabric variables and blend composition have on the burning behaviour of 20/80, 50/50 and 65/35 polyestercotton blended fabrics. Whilst LOI values were not dependent on ignition time, they were for a given blend composition dependent on fabric area density. "Lo" values determined at zero area density were little dependent on blend composition for the blends studied. EOI values, as shown previously for single fibre component fabrics, were dependent on igniter application times. It is considered that the extinction concept provides a better indication of the variations of flammable character of polyestercotton blends compared to the individual fibrecontaining fabrics.