Generally speaking, the prisons WILL allow hard backs (especially federal BOP inmates). But, we would encourage a call to the facility before buying just to be certain. Since you are out of the country, if you'd like us to inquire on your behalf don't hesitate to ask.
https://www.inmateaid.com/ask-the-inmate/i-want-to-send-my-fiance-some-books-form-amazon-when-my-fiance-was-in-county-he-could-only-receive-paper-back-books-is-it-the-same-in-prisonthank-you#answer
Accepted Answer Date Created: March 16,2014