bolster vs bolster up

bolster is a noun but bolster up is not a noun.

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

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

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

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