[gafftaper]

Real books are the way to go. I used foam to create the mattresses for an 8' tall bed in Once Upon a Mattress. It worked great. But it's really messy and it isn't all that cheap. The foam dust gets into everything. It creates quite a static charge. It's hard to cut accurately. It's a real pain... and I was only doing a bunch of random sized strips. I can't imagine the pain of trying to do it for a couple thousand books.

You are MUCH better off calling all the libraries you can find. Don't forge schools, colleges, universities, thrift stores, used book stores. You might get a used book store to loan you the whole lot in exchange for an ad in the program.

The other problem is how do you stabilize the stacks. If you are talking 6' piles of books they are not going to stay upright easily. If you can get books that you can destroy try running dowel through them to secure them together then screwing the whole stack to the floor.