bolster up vs bolster

bolster up is not a noun while bolster is a noun.

Word	Noun	Adjective	Verb	Adverb
bolster up	No	No	Yes	No
bolster	Yes	No	Yes	No

As verbs, bolster up and bolster are synonyms defined as:

bolster up (noun)	bolster (noun)
	a pillow that is often put across a bed underneath the regular pillows

bolster up (verb)	bolster (verb)
support and strengthen	add padding to
	support and strengthen
	prop up with a pillow or bolster