Just 2 pieces of 1" thick good quality hobby foam I cut to the exact size and shape of the spec for Medium SAPI plates; as close to exact as you get with foam anyway.  Never ended up using them in game, but I stuffed them in my medium Spiritus LV-119 and medium Crye JPC 2.0 and they fit beautifully and made the PCs look exactly like they have real plates properly fitted in, except these weigh almost nothing and aren't rock solid.  They bulk the plate bags more than enough to take out all the slop you'd get in an empty PC but are infinitely more comfortable than solid plates.

Have had a quick layer of black krylon, but the foam really soaks up paint hence some of the blue showing through.  Price includes postage which will be around £3.50, I just got the PTS fake plates so I don't need these and this price should work out cheaper than buying your own raw foam then cutting to size and spraying.