Well, I may be new to cosplay, but my first costume had armor that I made out of craft foam. It was tedious, but I couldn't believe how much I loved the result. I didn't do that great of a job on the costume, but I will tell you right now it's more durable then you think it is.
My sister punched the armor on my arm (her character does that) hard enough that it hurt a tiny bit, and it didn't leave a mark. I got glomped by about 5 or 6 people who weren't nice to the armor, and absolutely nothing happened. Nothing popped off or got bent out of shape. The only damage I got from it was when I stood in the rain talking, the water left slightly noticeable spots on the black.
Then when I moved it got packed by movers and is now bent out of shape from being in the middle of a big box, folded over itself for 2 months. But I can wear it and it only looks a little funny xDD That's off the topic.
I'm not sure what tutorial you looked at. Was it the one where you used heat to bend it to the shape, then glued on fabric backing, then painted a bunch of coats of glue and then paint over it? If that's the same tut, let me tell you, it works wonderfully!
Just don't let anything sharp poke it and it should last you! I wore it for 3 days and I was -not- gentle with it after the first xD That's all I can say about that, good luck ^^