Cats are drawn to boxes for a mix of instinctive and physical reasons. In the wild, small predators like cats are also potential prey, so enclosed spaces offer a sense of security, letting them observe their surroundings while feeling hidden and protected from threats. This instinct persists in domestic cats, which is why a cardboard box can feel like a safe little fortress.

Boxes also provide excellent heat retention, and cats prefer warmer temperatures than humans, often seeking out cozy, insulated spots. The snug fit of a box can mimic the pressure of being held or swaddled, which many cats find calming, similar to how swaddling soothes babies.

There's also a hunting angle: boxes make great hiding spots for ambush behavior, letting a cat watch and wait before pouncing on a toy, another pet, or an unsuspecting human ankle. Combined with reduced sensory stimulation from the enclosed walls, boxes can help lower stress levels, especially in unfamiliar or busy environments like a new home or a vet's office.