What does the author mean by "they were numb as if encased in a thick skin that nothing could penetrate"?

From the author's description, we can infer that Mama, Abuelita, and Esperanza are without emotion. If they kept themselves numb, nothing else could hurt them. Thus, they hardened and isolated themselves.... they didn't even talk about the fire, their situation, or the uncles to each other. There simply wasn't anything left to say.