Provided herein is a new fire barrier nonwoven composed of flame retardant (FR) cellulosic fiber(s) and untreated cellulosic fiber(s) and optionally a binder fiber and methods of making the same, wherein the FR cellulosic fiber contains FR chemical(s) or FR compound(s) that have melting point or decomposition temperature at 400° C. (752° F.) or below. The FR performance of the new nonwoven provided herein is comparable to the conventional FR nonwoven (FR cellulosic fiber/binder fiber), but has advantages in cost effectiveness.