Impassive is a synonym of unimpressionable.
As adjectives the difference between impassive and unimpressionable
is that impassive is having, or revealing, no emotion while unimpressionable is not impressionable.
impassive
English
Adjective
(
en adjective)
Having, or revealing, no emotion.
Still or motionless.
Synonyms
* apathetic, phlegmatic