Great question. They're in storage until Monday but yesterday I held one of them (which was A LOT of fun I should add) to see what the material is like.
First off there are two red velcro arm bands which allows you to hold the shield on your forearm which I thought was a good idea (so on Halloween, you can hold your trick-or-treat bag behind your shield!).
The shield is not very thick, like the hard plastic of a frisbee. But I won't go as far as say it's flimsy or easily breakable. I didn't get the idea that if you dropped it, the shield would break.
Keep in mind that Disguise seems to care more about how their costume accessories look more than anything else.
When I get a hold of the shields on Monday, I'll add anything here I missed to describe the shield. If you're familiar with Disguise's classic shield, the biggest difference between the classic Cap shield and this one is the red and blue colors of the movie shield are darker.
I hope this answers your question.
