http://www.ar15.com/forums/t_7_173/1570627_AR500_Armor_III__Lightweight_plate_set_w_Paxcon_Buildup__280.html
http://infidelbodyarmor.com/armor-c-1/level-iii-multicurve-lightweight-composite-in-stock-p-219
Steel or composite? Storage temps; temperature plates will be exposed to, storage handling in trunk of squad car, or at home, most ceramic plates won't handle being dropped or rough handling, weight of steel vs. ceramic or PE, ballistic ratings of the different types/materials. Sound as if you need to do some research as to your needs, wants, budget, capabilities, weight you are willing to put up with when wearing the plates and carriers, agency policy, work environment,etc., etc. Just buying a plate carrier and then asking about hard plates is putting the cart before the horse since some plate carriers won't work well with cetain types of plate styles, cuts or weights.