It's easy to cut cardboard. You don't even need a sharp blade, just a good stroke. Traditional Japanese cutting practice (batto-jitsu) uses bamboo wrapped in grass and soaked in brine - it's supposed to simulate a human body - those Japanese think of everything. I dabbled in batto-jitsu - we did a similar process using bamboo and pampas grass. It worthy of note that there is a wide range of bamboo, not just thickness and dryness, but many different types. If memory serves, we used bisetti and goldenrod bamboo, a few springs bound together.

Some blade makers still use rather rigorous tests, but cardboard certainly isn't one of them. At Shaolin, they cut nails.