stiffener vs filler

stiffener and filler both are nouns.

Word	Noun	Adjective	Verb	Adverb
stiffener	Yes	No	No	No
filler	Yes	No	No	No

As nouns, filler is a hypernym of stiffener; that is, filler is a word with a broader meaning than stiffener:

stiffener (noun)	filler (noun)
a member attached to a beam web to prevent loss of strength due to web buckling.	the tobacco used to form the core of a cigar
material used for stiffening something	anything added to fill out a whole
	copy to fill space between more important articles in the layout of a magazine or newspaper
	100 filler equal 1 forint in Hungary
	used for filling cracks or holes in a surface