He said it’s a wall that has the sun hitting it in the afternoon. If he has a standard 2x4 wall with fiberglass it’s only giving him an R value of slightly over 6. If he has 3 inches of foam applied it’s almost an R value of 20. That’s a huge difference on a wall the sun beats down on. That part will be noticeably warmer due to that. Also, if he’s not upsizing his A/C unit, there is that to think of also and a foam insulated room costs very little in additional AC. There really is no substitute for foam, and certainly if the price is the same. It will be 3x the insulation R value per inch, and the quietness is very different in a foam house.