I m planning on sewing helmets that look like ones from my favourite games/movies. What materials would be best? I.E Durable/stiff/not bend?
Look up something called Fosshape and Wonderflex It's used by costume makers to make lightweight but realistic looking helmets, armor and more. Here's the place that sells both. I use this place for corset supplies and they have lots of cool costume supplies: https://www.farthingalescorsetmakingsupplies.com/Wonderflex-and-Fosshape-s/1989.htm You can easily shape it while soft and then heat hardens it so it's stiff and durable. It's perfect for costumes based on games, movies and comics.
To sew on a machine. You would need to use interfacing to make the fabric stiff and hold its form.
kevlar and some eps foam, don't even ask how I know this sh*t lol.