Look, here is the reality of the situation; when anything is baking in the sun for an extended period of time, it is going to be hot. That is if the ambient temperature itself is hot, of course. Anyway, in the heat of the summer, there is a good chance that your chairs will get hot (especially the metal frames). However, while you are sitting in them, the heat should not be enough to force you to move (unless the sun is beating on you and you start frying).