Fuck me, that's such a good solution.

My flat has all windows facing west-southwest, and I live on the top floor under the roof. I've had 30 degrees inside when it's been 24 outside today. Tomorrow's going to go up to 29. I'm going to boil in here.

Bro I gotta ask... You don't live in Sweden by any chance?

I got 3 inch foam board from lowes and cut it fit my west facing windows.

Put aluminum foil on the OUTSIDE of Velux windows.

My friend's parents were velux installers the amount of windows they had to fixed that were burst or cracked because of people putting aluminum foil on the inside instead of the outside is staggering. The heat gets trapped in a very small pocket with the very heat conductive aluminum, the thermal shock can crack it.

The sun is putting out roughly 1kW/m^2, so for every square meter of your roof you cover, you're keeping out 1kW of heat (obviously not strict math here). You can decide if you are more concerned about looking crazy or suffering in heat. Emergency blankets, space blankets, mylar(they're actually polyester) blankets, are cheap.

small trick: put it on the outside.

Most modern window glass heats up as it filters out UV and a few other light bands. My previous flat had windows that would go as high as 95C!

All that heat WILL radiate inwards and through the foil.

if you out the foil outside, you prevent that heat buildup and radiation.

You can also buy cheapo reflective film you can install on your windows permanently, for the same effect.

I use emegency blankets. They also work and are more robust than aluminum foil. They are also cheap.

Everything reflecting shoud be attached outside the window, since the reflected heat can result in shattering the window glass.

Why is this a shitpost? For lack of anything else, this works.

I use this product on all the windows in the summer and winter. It insulates a bit and also reflects back.

The one thing better than inside is to have something on the outside, but that’s not possible for me, because it gets really windy here.

Another heatwave life protip, put damp towels in the freezer and then sleep under them instead of a blanket. Use more than one so you can rotate out. Rolling them up will maximize freezer space, but I've also just wadded them in there as well.

Just get a roller shutter. I have a similar roof window and mine was like €40 with some DIY, which was years ago and has saved me tons of headache

If the foil gets warm, it's heating up the space like a small radiator, right?