PVC Piping
I bout a 10 foot peice of 4 inch (or 6 i forget which) pvc (1/4 thickness) for about 5 dollars and was able to make almost my entire suit out of it.
The thickness of the peices gives you much more of an armored feel while wearing it. (though heavier and velcro may not be the best option for attatching.
Lets take for example the two breastplates. Cut them out then mark how long they are on the pvc.
Cut the PVC and cut a line from one end to the other so you can roll it flat.
Heat with about 300-400 degrees in your oven on a cookie sheet.
when the peice starts to bend grab it and flatten it out, have weights or some heavy objects to place on it while it cools and BE SURE to have pressure on the edges.
The peice may not cool 100% flat but it will be very close depending on how much weight u applied.
Place your tempaltes on (you can fit 2 XL breastplates on there if you) When placing your templates be sure to go WITH the curve of the pvc piping. Otherwise it will still try to warp back and it won't come out right.
Cut out your peice with a jigsaw (worked best for me) and any details, like the digital display in the plate, with a dremel.
Lightly sand the peices to remove PVC "dust" that forms on the cut lines
Reheat the peices at 300-400 degrees and once they are soft again (starting to curl) they are ready to form. Be sure you have your flightsuit on because your body will be slightly less curvey and the peices will not fit right if you try to place them on without it.
PVC is very durable and easy to work with. It is readily available, (unlike trying to find a plastics shop).
PVC is NOT GREAT for trying to create sharp edges, though using a thiner pvc (1/2 inch or below if available) it may be doable. The small amount of non-flatness that will probably form gives the armor a bit more "used look" once painted.
**BONUS** Unless you live in the desert, you don't have to worry about your PVC warping if you leave it in your car and it gets too hott!
This is a picture of the 3/4 inch PVC, doesn't that look like it could take a beating?