Wonderflex is a sculpting material that's basically a heat-moldable plastic sheet with a fiber backing. It sticks to itself really well, so multiple pieces can be fused together, and it's easy to shape with just a hair dryer or heat gun. It's used a lot for making Cosplay armor or other "hard" costume pieces, but it's lightweight, paintable, sandable and really easy to work with.
I didn't have a project in mind - I just know that multiple times in the past, I've wanted to make accessories or costume pieces that are harder or more armour-like than fabric can be, so I ordered a sheet of it, and I'm having so much fun.
I wanted to start simple so I decided to do a Sleeping Beauty crown for my first project. It's a simple circle without a whole lot of shaping, so I figured it'd be a good learning piece. It turned out just gorgeous. :)