Do solar curtains actually work and cool off a hot room facing the sun?

They seem to. Here are some comments:

“It cut the Houston Texas heat in the bedroom 8 eight degrees from 80 to 72 in the early morning sunrise, you did not wake up early, because you were hot.”

“We live on a lake and the wind gets rather rough in the winter in our lakeside sunroom. These solved my problems with the cold in a room with windows floor to ceiling. It has also been really hot this summer and the curtains have reflected the >100 degree temps really well.”

“I have truly enjoyed the solar curtains and my engery bill hs decreased.”

“These solor curtains have made a world of difference. Keeps the sun/heat out making the kitchen about 10 degrees cooler.”

Source

I haven’t used them, but I’ve found that just keeping the sun out helps a ton. My last apartment faced west and got the afternoon/evening sun, and when we kept the blinds closed it made a world of difference.

I think you could probably get a similar effect with blackout curtains.

I use room darkening/thermal curtains and they help a lot in summer and winter. I have never used the thin silvery kind. Is that what you are asking about?

They help a lot in reducing the energy absorption through that window. But without active cooling, the indoor and outdoor temperatures will eventually equalize, regardless of the insulation or reflective material or other passive methods to keep the heat out.