Took this technique I learned in prison to make it bearable during the heatwave:
- Wet the window with a sponge or rag.
- Put aluminium foil up against it. Shiny side out. Cut beforehand on angled windows like that or use the roll on vertical surfaces.
- To cover the overlap, just wet the foil already on there, but be careful not to pull it off at the edge. An overlapping strip will stick to the other ones.
- Use masking tape to cover any overlapping edges that come away, as well as the edges that have a hard time connecting to the windowsill.
This keeps out an incredible amount of heat; you can feel how hot the foil itself gets during the day, while keeping the inside nice and cool.
Yes but by reflecting >95% of the light, it does not get nearly as warm as what the light would otherwise shine on. Also, if placed outside a multi-layer window (which you should or the window may overheat and crack), the heat exchange to the inside via convection/conduction is stopped, only radiation remains, and the 80°C foil radiates way less than the 6000°C sun.