Hi,
I wouldn't do this.
I use shade cloth out in the garden to protect certain plants from too much sun.

However, your containers are closed, so putting the shade cloth on top may actually make them hotter.

Instead, I would make your holes on top larger, even take the top off, or halfway off.
Then, at night, or when/if the temps drop, you cd put top back on.
Depends on what is growing.
What are you growing?
Also, now that I see you are in Z7, you may soon be able to leave the tops off completely.

Another solution wd be to put the containers in dappled shade, or total shade for the hot part of the day.

hope this helps,
ellen

I did this, sort of, when it got way too hot and I didn't want my already totally open containers to fry in the afternoon sun. I used a piece of white tulle, and it worked really well. I just draped it over the containers. It lets the air through, but kinda creates a dappled shade. (I know it worked because one poor plant that I forgot to cover fried and the rest were fine.)

Leisa