The key is not to let the heat in in the first place during the summer. Thick external shutters do wonders in that regard. Well insulated windows alone will let

The key is not to let the heat in in the first place during the summer. Thick external shutters do wonders in that regard. Well insulated windows alone will let in the heat (in form of light) but not out again (IR). I really wonder why these shutters are not way more common than they are.