To answer your question, yes those foam boards are just strong enough to make armor... make sure you cut cleanly and glue properly, hot glue is used very often and seems to work observing foam users' work.
This really doesn't need to be stickied, let alone be it's own thread. No offense, but it's just not as important as you think it is. Whenever you have a question, why not try finding out yourself? Trial and error is the best way to learn, especially with these topics. As a community put together, we don't want two million question threads, you see... and these add up. Ask in the Help! for... threads in the noob forum.
I'm telling you this because you shrugged off your first reply as "unnecessary" and I found to be rude. Please, mate... manners.