protective shells

Protective shells are hard outer coverings that shield vulnerable organisms or objects from harm.

In nature, creatures like turtles, mollusks, and crustaceans develop these structures for defense against predators and environmental hazards.

The term extends to any rigid casing designed to guard what's inside, from phone cases to armored vehicle plating.

Figuratively, people build protective shells around themselves emotionally, keeping others at a distance to avoid hurt or vulnerability.