In the case of books, the product with value is the content (the words), not the packaging (the pages of the book). Books are very recyclable, though. The question, really, is what about clothes? Well, it turns out textiles are recyclable as well. That’s what happens to most clothing that’s donated to Goodwill etc. - if they don’t sell, and let’s face it, who wants most threadworn, out of style clothing?— then they’re shredded & recycled.