If you have had the opportunity to observe a cat for some amount of time, you have certainly noticed that cat’s like cozy spaces, and will take the opportunity to get into empty boxes whenever they can. So, why do cats like cozy space, but more specifically, boxes?
The simplest explanation is that cats are naturally curious creatures that enjoy experiencing new things, and since boxes are not generally common in common living areas, once discovered become a point of interest for the cat, and they explore their new found toy by hiding behind it, cozying up inside it, and even using it as a scratching pad. However plausible, this explanation is not the best as almost any animal (even children) are attracted to anything new in their environment, especially empty boxes—even children seem to be more interested in an empty shipping box than the toy that came in it.
Safety & Comfort
Who doesn’t like curling up in a cozy location and taking a nap? Cats spend a fair portion of their day resting or napping, and prefer a place where they can feel safe. A nook, or in this case a box, provides that safe space where they feel as if they have a fortified place to rest where no potential predator can sneak up on them (since there is just one opening). This is an instinctual behavior and has stayed with the cat despite domestication and cohabitating with humans for thousands of years. A box also seems like a good place for a cat to lay in wait for prey. Even though there is very unlikely that a mouse will scamper across the living room floor, your cat may still take the opportunity to hide out in a box waiting for just such a moment.
Scratch that Box
Empty boxes make great scratching posts (although temporary ones) for cats, and since cats love to scratch an empty box is a great invitation for play. Cats scratch in order to keep their claws sharp, and also as a means of marking their territory by secreting scent from glands between the paws.
The Calming Effect
Research has shown that resting inside empty boxes has a calming effect on cats. In fact, it has been shown that cats in shelters that are given empty boxes to use as they please are significantly better acclimated to shelter life than the ones without boxes. This is a very helpful finding since cats, unlike dogs, have a tough time getting used to a shelter environment, and generally exhibit signs of stress when in shelters.
Adding the box to their environment allows the cat the hide inside the box, and become acclimated with the new environment at her own pace reducing the impact of the stressors that a shelter life inevitably introduces into their lives.
Big Cats Love Boxes Too!
This video from bigcatrescue.org shows how big cats, like their domesticated cousins, enjoy empty boxes. They play with the boxes, rest in them, and act like one would expect a house cat to act.