Just wanted to add ..don't count out cardboard so quickly.

They are making houses and bridges out of the stuff now a days.

In advertising cardboard signs have been used for years and that's outdoor use!! I have a sign from a building contractor that did work on my house that is printed on cardboard and sat outside for more than a year with no visible deterioration.

I would love to know how they weather/waterproof the stuff.....If anyone finds out, please let us know.