Another beginner question

I'm pretty new here myself. I've got two helmets in the works and have learned a lot in the process.

The first I started off intending to use posterboard impregnated with fiberglass resin. It works but is pretty heavy. I ended up adding fiberglass cloth as well but it's quite sturdy. For the outer layer I used sheet styrene from US Plastics. I believe it was .6mm... With shipping it was like $12 and is enough for two or more helmets

The second I eliminated the posterboard and used straight styrene. I did use some thick, non-corrugated cardboard for the forms inside the dome, but most of that gets cut out after the dome's done. I reinforced this one with fiberglass as well.

One thing I will add is that I wouldn't recommend going the route of using posterboard and resin. I tried it in making a cod piece as well as knee armor and the posterboard serves as its weak point. It'll flex enough to rip the whole thing apart. I don't think it'll be a problem on the helmet but everything else I tried worried me enough I won't try it again.

That said, I HIGHLY recommend making a prototype out of posterboard before you do anything else. It's dirt cheap and you learn a lot from it instead of making mistakes using your more expensive plastics.

where did u get the poster board is that something that can be bought easily?

Around here I can buy posterboard at most grocery stores and for certain any craft shop. It's dirt cheap.