my first idea is using a fur like this
but having the fur point upwards instead of down.
my second idea is using colored wool roving but im afraid it will felt itself when washed/moved around.
i could felt the roving into fire shapes but again i worry the washing will make it smaller/tighten it/misshape it.
ive seen hard plastic being used for cosplay fire but id like it to be able to blow with the wind like real fire instead of a static shape.