Back up Calibre Library but only epubs

I have a 13000+ book library started many years ago when Kindle didn't allow epubs.

I'm now storing epub, mobi and in some cases azw formats of every book.

I want to freeze my library with a backup and then create another backup of epubs only. I know I can save to disc but I'm concerned I may lose some of my in Calibre formatting if I import them back to a new Calibre Library.

How can I do this safely