Ok, So I'm working on my helmet still and I've decided to go with bondo for the exterior but is there something else I could use besides fiberglass?

Also the interior is all lined with black hockey tape for now but I'd like to have something better for it. I've herd of people using resin but I don't know what it is or if it's a spray on or paint on product and if I get it from a hardware store or craft store?

So can I use resin for the inside or is there something better I can use? Let me know you thoughts guys!