Hello Smufter
Framey beat me to it ! .
I don't fish in France , and when I know it's going to be a scorcher I either do an evening session , or an early morning session and pick a swim that offers me shade - yes I know Yonny I should be choosing my swims on where the fish are , but I don't want to melt ! .
However , I have got a Skull Cap for my brolly which I took off as you need to take more care putting the brolly up and taking it down ( I broke the brolly in my haste to open it up ) ; so I'm going to keep the Skull Cap on permanently and see if the double thickness of material ( and the peak ) stop , or reduce the problem you talk about .
Failing that there's lots of trees around my lake ! .