Can I go back and ask an ignorant question?
Where do you get mylar? And are there websites where I can learn to reinforce books? I have two little ones who absolutely love books to pieces right now. I don't want to discourage the book love but they are still a little too young and hyper to remember to handle gently. Some prevention might be useful. The scotch tape is just not cutting it.
When I was working, I just bought it from the library when we ordered it. I didn't use it much because I don't think it is good for much except enclosing book jackets.
When I was in college, I covered all of my frequently used paperbacks and the ones my mom used when she was creating a course to teach with Clear Contac (shelf liner). It doesn't take much experience or imagination to figure out how to do it. That's what I used to cover the paperbacks in the media center where I was librarian, too.
You can buy 3M library tape from the office supply store. That's what I still use for spines and to reinforce where the covers of books meet the first page. I just used it the other day to repair our travel atlas that we use when we..........travel. We try to use them for about 3 years, and, wow! do they get worn! I also remember using it a lot to repair boxes of beloved games the kids used. It's better than packing tape by a long shot - sturdier and easier to handle.