Help: What Material Should I Use for Armour?

I'm on a budget, and I'm trying to figure out what material I could use that's lightweight and could look convincingly like metal. Trying to create a chest piece and maybe some segments for the arms.

EVA foam floor mats are a good option. Check out Punished Props on youtube if you want to learn how to use the stuff.

I like SIntra because it is cheap, super light and easy to cut, glue, sand plus it takes paint really well. Sintra gives off hazardous fumes when heated (for bending), so you need to be careful and use a respirator -also when sanding. There are great videos on youtube on how to use it.

This link shows some simple chest armor made with sintra for one of my son's costumes...

https://www.therpf.com/showthread.php?t=283373

Worbla is fun, but a bit expensive and heavier.

A lot of people do amazing work with EVA foam.

I personally prefer plastic as a stand in for metal because it is more rigid than foam, but that's just my preference.

I second EVA foam. It's cheap, easy to work with and can be painted to look convincing as a "10 ft prop" (Looks great 10 ft out).

Watch Evil Ted's tutorial on making clean seams and painting.

Another +1 for EVA foam. In addition to Evil Ted's tutorials, Bill Duran over at Punished Props has a bunch of fantastic tutorials on making armor, and even has a couple books on the subject.

Edit: totally missed Bill's tutorials were already mentioned. But seriously, some really good stuff for getting started over there.