Because it's literally the perfect material - and we've considered all of them. First of all, there's nothing cats love more than cardboard - this is known.Nothing else has that delightfully smooth-rough texture and makes that heavenly scratchy sound when you claw at it. Nothing!! Our cardboard is reinforced and extra durable – meaning it has no problem holding up hefty cats (or even several) sitting or jumping on top of it! As a bonus, it makes the puzzles lightweight, enabling them to slide around - adding to the challenge and amusement.Scratchy, strong, light and eco-friendly - that's what makes cardboard the material cats and planets love most.