I bought a box of these envelopes to mail out several copies of a book. Perhaps padded envelopes would have been a better choice for books, but they are much more expensive, and since I had to mail quite a lot of copies, I settled for these.
The heavyweight brown envelopes are 9 X 12. I took a copy of the book with me to the store to make sure it would fit well, and these envelopes were just right, the book fit very nicely without sliding inside. The envelopes are closed with a two-prong metal clasp for additional security and sealed. I also sealed the flap with some scotch tape, just in case.
All the books I had mailed traveled very well in these envelopes, there were no bends or any other damage. There were 100 envelopes in the box, so I had a lot left over; I continued to use them to mail anything larger than a regular business letter that could use some extra protection. I am very pleased with these basic, not overly expensive, good quality brown envelopes.