Fiberglass: inside, outside, or both?

Hi guys. I'm, about to purchase materials for my first build. I'm using paper and cardboard (chipboard actually, not corrugated cardboard) for the original structure, and I plan on applying fiberglass for strength and bondo before priming. My question is in regard to the fiberglass.What does the community recommend as far as applying it to the inside or outside of the helmet? I don't want any of the form details to be lost, but I want it to be strong. Are there any other strategies I should be considering?

I've seen tutorials where fiberglass was used on top of the paper or cardboard, either on the outside or inside of the helmet, and I've seen someone mention doing both. As a result, I do expect to get a couple different answers. Every bit of input will be appreciated.

Thanks!

With my scratch builds I apply bondo to the outside and sand smooth then repeat to get the desired contour. Then i brush on resin to the outside to seal it. You have to either heat and cool over and over with a hairdryer or spray with a light coat of primer to get it to cure all the way. then sand the outside smooth. It will be sealed hard as a rock. Some guys use glue or polyurethane which I'm sure is fine...I just like the durable feel of polyester fiberglass resin. Keep in mind it's a lot harder to sand, but no pain no gain.

At some point either before or after coat the inside with resin and then start laying in fiberglass matt and "wetting it out" completely to get any air bubbles from underneath it. You can break the matt into sensible pieces with a little overlap patchwork. don't mix more than 3 or 4oz at a time or you will probably waste some resin. Also, get a real paint/chemical respirator so you don't trash your health in the process. Polyester resin fumes are a big pile of nope.

You can do a second layer if you want more strength.

You can search how to fiberglass on youtube if you want to get more comfortable with the mechanics of the process. most of the vids are for boats and motorcycle parts, but at least you can see how it all goes together.

Thanks for the info! Looking forward to getting started.