I am insulating both my coops. this past winter was brutal on us in CT sub zero temps and all of them got frost bitten on their combs. sure it grew back I just felt bad for them so bad in fact most days they stayed inside the coop by their choice.
Insulation actually keeps the sun from heating up a building, unless you have lots of double glazed windows to let the sun in but keep the heat in........I think by insulating them it will help keep some of the day warmth from the sun ........