One way insulation does not exist. If your house is insulated to keep the heat inside, it is also very good at keeping the heat outside / cold inside.

Also tangentially many Europeans seem to be confusing insulation with inertia, saying their house is correctly insulated against the heat when in fact it’s just a stone building that is taking more time to heat up. At the extreme you have European churches buildings that are very badly insulated but stay cold most of summer because of all the stone mass.

One thing Europeans have yet to realize is that good insulation only works when the nights are cold enough to evacuate the heat before it reaches the inside, and that during a strong heatwave there is no adaptation possible, AC is needed.