If someone is impassive or their face is impassive, they are not showing any emotion. He searched Hill's impassive face for some indication that he understood + impassively im·pas·sive·ly The lawyer looked impassively at him and said nothing. not showing any emotion
having or revealing little emotion or sensibility; not easily aroused or excited; "her impassive remoteness"; "he remained impassive, showing neither interest in nor concern for our plight"- Nordhoff & Hall; "a silent stolid creature who took it all as a matter of course"-Virginia Woolf; "her face showed nothing but stolid indifference"