Depending on location, insulating an above ground pool can make sense.
- By retaining heat in conjunction with a solar cover you can extend the pool-use season on both ends.
- Where you install the insulation is as important as what you use for insulation material.
Wrapping the pool walls with insulation
In my opinion I would not consider either the material recommendation or placement to be good ideas.
- Any insulation wrapped on the exterior of the pool that acts as a vapor barrier may result in your side walls rusting out quickly by trapping moisture between the pool wall exterior and the "bubble" wrap insulation.
- Depending on the climate zone you are located in the insulation value of bubble wrap is questionable (in this application).
- Wrapping the exterior walls in fiberglass would be unattractive and ineffective once it became wet (rain or splash over). Same issues exist when using spray-applied foam insulation.
A supplier of bubble wrap insulation recommends (here) that it be installed under the liner. I think this product is great as a liner cushioning material be fairly ineffective as an insulation material when temperature differentials are high (between ambient/ground and pool water).
Add insulation on the inside
The proper way to insulate an above ground pool would be to add insulation to the inside of the pool walls (and ground) prior to installing the liner. Two inches of foam would be effective but it would need to be custom fit to make sure the liner fits properly.
This page (here) provides information on insulating under the pool liner.
Or build an enclosure
Another consideration would be to build an insulated enclosure around the pool. This would look terrific but be the most costly approach.
This would leave a space between the insulation and the pool walls so you wouldn't need to be concerned with condensation and premature rusting of the metal wall panels.
I recommend that you consider waiting to insulate until you replace the liner, then opt to install foam insulation under the liner as described above.