Dfndr Armor has been making armor under their parent company for the military. Their composite armor is lightweight and they offer various protection levels.
The armor below is for use in a backpack and it only weighs 3.2lbs. This one is rated for .308 win, just not AP rounds. The armor is a polyethylene based polymer and that is why it is so light weight.
They come in varying sizes and they have a couple designs for popular backpacks like Vertx and GoRuck.
If you only need handgun level protection then the armor is as light as just one pound. Their handgun armor costs anywhere from $150-$215 and the rifle grade armor is anywhere from $395-$700. It all comes down to what level of protection and that determines the materials used.
Their SAPI plate only weighs 2.5lbs!
Green tips will defeat their composite armor but they are currently working on next generation designs for the DOD.
For their level 3++ armor they use a protective layer followed by a ceramic.
They are also making their own plate carriers.