Cat furniture has never been so fun! We all know cats love playing, hiding, nesting, stalking, and sleeping in almost any box. These industrial-strength boxes are made from incredibly strong Corrugated Ultraboard™ which is recycled, recyclable, and uses vegetable-based ink. Catty Stacks secure to each other forming stable structures and can be easily moved and rearranged, helping maintain your cat's interest. Create climbing structures to promote healthy exercise. Excellent for multiple cats.