Hi Andy, I lost the weekend to Sebastian and Clay, but let me answer your original question. The difference between a regular plastic bag and a hermetic GrainPro bag is that a regular plastic bag is more porous, allowing in oxygen which enables the insects to not only live, but thrive.
A GrainPro bag has a barrier layer, stopping the inflow (and outflow) of air. Insects suffocate to death after a few days. A hermetic GrainPro bag is 500x more airtight than a regular polyethylene bag. It's more expensive than a regular plastic bag because of this barrier layer.
Regarding mold, as long as the cocoa beans are dried to the right moisture content (about 7%), they will store perfectly well in a hermetic environment. The key is drying the beans properly (7%) before putting them in the hermetic environment.
You sound like you have a mess on your hands - but hermetic is a great way to control for infestation. We have users all over Latin America and the Caribbean using GrainPro to both store and ship their cocoa beans - organically. Happy to put you in touch with any of them.
If you have a quantity above 1 metric ton - you could also consider using a GrainPro Cocoon and flush (organically) with CO2 to kill the insects. You can use this method wherever you have access to a CO2 cannister (most countries of the world).
Hope this helps. Let me know if you have any other questions,
Jordan