I'm thinking of using ( aluminium strip type etc..) , as a third and final layer ; I am having problems keeping temperatures down ( already) this year despite ventilation, extractor fans, humidification, etc.
I do have a big turbo fan - 20 inch diameter , hollow blades, spins at 10,000 rpm, water fed into the blades and thrown out centrifugally produces tremendous stream of moist air, and this can bring the greenhouse temperature down by 5 degrees C in half an hour - but the problem is the noise - makes the neighbours complain . One says he has measured it at 146 decibels - which I find difficult to believe, but whatever, I cannot use it again..

But the problem with the aluminium stuff is that there is no edge or end reinforcement, no eyelets, no easy way of fixing , and where I live, we do at times ( around the equinoxes) get gales sweeping up the English Channel - which separates UK from France , and I live a mile from the sea. 100mph winds ( 160kph) are often measured at the nearest weather station, 10 miles away. So although I have a sheltered garden, its all relative ! So I need to fix the shading very well, else it will blow away in the first gale.

But how ? I have some ideas, and I'm looking for more, especially from anyone who actually uses the stuff.