Window fans and blocking out light

I need a way to cool the room down when the AC isn't pumping. I was thinking of getting a nice window fan. maybe something like this? www.homedepot.com/p/Lasko-16-in-Electrically-Reversible-Window-Fan-2155A/100405673 But its not exactly built for my window. I can probably make it work, but does anyone know a good way to blackout the window so my neighbor doesn't see any lights? Would black construction sheeting from the hardware store do? They have 4mm thick and 6 but the difference in price is huge. Does anybody use it? I was going to go with a large cardboard cutout but the sheeting sounds easier.

I'd back some cardboard up with the sheeting....The sheeting blocks enough light to fool a plant, but there's still a faint glow that would just look out of place through your windows.
I'm in the same situation.
And maybe put some ornaments etc between the window and sheeting if you're disguising a bedroom...or old car bits, tools etc if you're growing in a garage. A black, blank window can raise suspicion

also to make it so you can't see the black plastic home depot and lowes sell rolls of fake plastic stain glass ... its like a plastic overlay for windows with designs... you can put that up then put black plastic behind it and no one will know the difference it will just look like you added some "class" to your window..

I'm sorry i just saw i mis read the post.. you wanted to cool it when the ac isn't pumping.. my bad on that.. but the winnow covering will block the plastic.... sworth is right the black plastic is a give away that somethings up