Let me give you a whole bunch of good reasons why cardboard is an excellent choice for crafting with.

1. It's Free and Everywhere. You can get lots of it just about anywhere and in all kinds of shapes and sizes. If you buy things online you have an immediate and regular source of it. And even if you don't buy it online you can get plenty of it from neightbors or even from your local stores. Just go down to a local store and ask if they have any empty boxes. They sure do.
2. It's very easy to work with. You can cut it with a plastic knife even. Really. A company called "Makedo" sells a whole series of tools to use with cardboard. Here is their plastic saw knife. The Makedo tools are all available on Amazon here: Makedo
3. It is very strong. It can sustain a lot of weight and pressure. That is why it is used for shipping.
4. It can be curved and shaped. Yup, it sure can. You just need to know the techniques for doing it. I have all the techniques on my website.
5. It can be hardened and preserved for long term use. Using Shellac or Mod Podge will harden your cardboard project and make it pristine for years, keeping the colors nice and fresh too.
6. And finally, it can be recycled. Cardboard is the most recycled thing in the world. It has a higher percentage of actual recycling than plastics. This is for a couple of reasons. First off it is just a form of paper. And secondly there is no glue in it.! The binding agent that keeps the cardboard together is actually starch. And that starch is water soluble. So, it is easily broken down into paper fiber with the starch removed.
7. It's easily stored. You can cut open those boxes, lay them flat and store them anywhere. This gives you an instant supply. Start saving cardboard today. You are going to want it!
8. My favorite thing is the creative potential in cardboard. Box shaped projects, projects inside boxes, projects for cardboard cut from boxes. And so much more. Furniture, desk items, toys, machines and anything you can imagine.
9. So, have fun making things with the remarkable thing called cardboard!
10. Here is a picture of that Makedo cardboard knife/saw: