The word "more unimpressible" implies a lack of susceptibility to being impressed or affected. Antonyms for this term could include "impressionable", "open-minded", "receptive", and "sensitive". An impressionable person is easily influenced or affected by outside factors, while an unimpressible person is not. Someone who is open-minded is willing to consider new ideas and perspectives, rather than being closed off to them. A receptive person is willing to listen to others and take in information, rather than brushing it off. Finally, a sensitive person is able to detect and respond to subtle changes in their environment, rather than being unaffected by them.