[Electrodynamic]

I would maybe use the foam, but that's about it. You'd have similar results lining the back wall with fiberglass insulation. I can't stand fiberglass because it's messy and I always end up itching afterwards, so I'd use the foam. But like I said, these kind of treatments are largely beneficial behind midwoofers (midbass and midrange), but not that beneficial to subwoofers in small sealed boxes.