radiant — emitting rays of light; shining; bright: the radiant sun; radiant colors.
insusceptible — not susceptible; incapable of being influenced or affected (usually followed by of or to): insusceptible of flattery; insusceptible to infection.
obstinate — firmly or stubbornly adhering to one's purpose, opinion, etc.; not yielding to argument, persuasion, or entreaty.
stubborn — unreasonably obstinate; obstinately unmoving: a stubborn child.
unimpressionable — easily impressed or influenced; susceptible: an impressionable youngster.
unresponsive — responding especially readily and sympathetically to appeals, efforts, influences, etc.: a responsive government.