The present invention relates to a flame resistant thermal liner comprising a nonwoven sheet comprising nanofibers of a synthetic polymer having an limiting oxygen index of at least 21, a mean flow pore of 10 micrometers or less, a thickness air permeability of 25 to 6000 cubic feet per min - micrometers (12 to 2880 cubic meters per square meter per min - micrometers), and an average thickness T1 : and a thermally stable flame resistant fabric attached to an outer surface of the nonwoven sheet, the fabric having an average thickness T2; a surface of the thermally stable fabric being in contact with a surface of the nonwoven sheet; wherein T1 and T2 are selected such that the ratio of T1 to T2 is less than 0.75. The invention also relates to a flame resistant composite fabric comprising the flame resistant thermal liner and a garment comprising this flame resistant composite fabric.