I live in a rental on 4th floor, unfortunately I can’t add anything to the outside of the windows… And putting anything on the inside risks trapping the heat in the glass and cracking it.
As long as there is no space for air to get trapped between the glass and a reflector, it’s no issue to put it on the inside (although its more effective when on the outside) - those foils that can be put on the window using a little bit of water do a good job. Biggest problem are dark objects when only away a few centimeters from the glass - those will crack the window in no time.
At least where i live, non-permanent modifications that use things like suction cups don’t need approval from a landlord.
I’m Dutch and in a similar situation. There’s these stick-on sun screens with suction cups: https://huizedop.nl/wp-content/uploads/2025/06/novalux-zonwering-met-zuignappen.jpg
Works wonders, can be made to size, they’re relatively cheap. Hope it’ll help.
I live in a rental on 4th floor, unfortunately I can’t add anything to the outside of the windows… And putting anything on the inside risks trapping the heat in the glass and cracking it.
It’s fine to put aluminium foil on the inside. Sunlight is reflected out without heating up the glass. That’s what worked for me anyway.
As long as there is no space for air to get trapped between the glass and a reflector, it’s no issue to put it on the inside (although its more effective when on the outside) - those foils that can be put on the window using a little bit of water do a good job. Biggest problem are dark objects when only away a few centimeters from the glass - those will crack the window in no time.
At least where i live, non-permanent modifications that use things like suction cups don’t need approval from a landlord.
Great stuff.