One is GacoFill slow-rise spray foam. Holes are cut into the drywall, and this foam is injected into the holes in “lifts.” This process requires an empty wall (no fiberglass). When completed, you have a foamed wall that is much more efficient than a fiberglass wall.
So what do you do if the wall already has fiberglass in it? That’s tough. You are stuck with an inferior product. What can be done is cut a trench in the center of the wall (from about belt height to chest height) and remove that strip of drywall and then remove the fiberglass from the wall completely. Then the wall can be filled with GacoGreen open-cell foam, the drywall replaced, and the house becomes much more efficient.
Get foam, and stay warm! (or cool).