The lightest material to use is probably cardboard......not the best material but people have used it and created some fantastic pieces. Full armor even. The next lightest would be EVA foam. So what other advise are you looking for?
EVA foam if you're looking for lightweight and durable. And it depends on whihc spartan 4 armor you are looking for. The armory has lots of files you may find useful: Halo 5: Guardians
If there isn't a foam version of the file you can always convert the pep ones into foam
Starfleet Spartan.........That has huge potential. not an ODST......that is too military looking. Starfleet is more exploratory rather than military.....or should be. Just imagine how boring a series would be if there were no conflict and just exploring things and planets.......That's why they have battles with....whomever. So which Spartan suit is least military looking but would be worthy of Starfleet?.........I would say that the 3 most non-military looking are:
How ever the helmets visors of these suits are smallish, that is to protect the wearer....in all of the Star Trek films, the EVA suits had large visors.....obviously to see the actors face on film....so you need a helmet w/ a large visor.......ergo, the EVA helmet......just not w/ the scratches like Emile's.
This is neat. I think recruit is more of a universal could be everything armor, and warrior is hold the line bunker down and be the backbone in a fight to me. I think the best helmets are tracker and pilot, but the one that nails the picture for me is the halo 4 oceanic helmet. As for armor, I think it would look best custom. Since it is probably something sleek like in the pictures above, I think nightfall or spi
I think I'm leaning twards spi armor with pockets? Oceanic helmet definatly.
If you are thinking more of a spartan IV look, athlon is also an ok idea since it is very round with minimal detail
Asking for advice is fine......but as I said, in the end, its all up to you. You have a ton of people here that will help you in any way we can for you to get you suit built. Whatever variation of mash-up you choose. Your suit is your suit. Build it how you feel it should be built........damn it......I sound like an infomercial for self help. Now I just have to get people to pay me to just listen to me rant......How they get people to do that is just beyond me.......
On a serious note....and to not totally derail a new member's thread...
I'm a huge Trek fan so....I think a Starfleet Spartan would be awesome.
I'm currently building out of a mix of foam and 3D printed parts. I like the accuracy of 3D printed but foam gives you less weight for sure, and with practice and patience (something I do not have) looks fantastic.
So I'd vote start looking at the foam route. Once you know what mix of parts you want and find the files of course.