I have a build thread documenting the progress on the 405th forums if you are interested! (Let's hope this link works)
https://www.405th.com/forums/threads/halo-ce-marine-cosplay.49790/

Basically, most of it is just EVA foam, with an op-shop bought BDU and a couple of bits of 3D printed parts. I've also recently 3D modelled the armour from scratch, with the intention of printing it one day

How did you make it? I am very interested