Help: What material is this and how can I do this?

Good day,

I have put together some costumes in the past. But I am wanting to recreate a helmet/head piece with simplest materials as possible. I spotted a person on Twitter that posted a production picture. I am wondering what material she used; any advice would be great. And any recommendations on how to easily create this "round" like head piece structure inexpensively.

I have experience working with resin/ pepakura. However, I am trying to avoid that if possible. The materials below dont look like resin, more like some foam like. I am not sure... There is an obvious bond in the middle of it where it appears it was bonded materials (not sure again)

The headpiece is from a fortnite character - Cuddle Team Leader

That's two large polystyrene (Basically a more compressed styrofoam) half domes glued together.

Each one should only cost about $10-15. You can find them online or at your local craft store, usually around the floral supplies.

Thanks so much TheNickFox

im doing a Fortnite costume cuddle team leader.

yay.....you have a build buddy cyberpyot