(pronounced ihm-per-TER-beh-behl)
When you are perturbed, you are anxious, worried, and uncomfortable, so it would stand to reason that imperturbable means serene and characterized by calm and composure.
Example: Due to Jessica’s imperturbable nature and sharp wit, she and her team were able to salvage the prospective client interview after a disastrous first impression and land the 50,000sf office remodel job.