thermal barrier vs boundary

thermal barrier and boundary both are nouns.

Word	Noun	Adjective	Verb	Adverb
thermal barrier	Yes	No	No	No
boundary	Yes	No	No	No

As nouns, boundary is a hypernym of thermal barrier; that is, boundary is a word with a broader meaning than thermal barrier:

thermal barrier: a limit to high speed flight imposed by aerodynamic heating
boundary: the greatest possible degree of something

Other hypernyms of thermal barrier include bound, limit.

thermal barrier (noun)	boundary (noun)
a limit to high speed flight imposed by aerodynamic heating	the greatest possible degree of something
	the line or plane indicating the limit or extent of something
	a line determining the limits of an area