Thanks all for the answers.
Actually I always use a very thick mulch. The thing is one year I used some big flat stones which were around, covered the roots area with and used strawmulch on top of it and it really helped to prevent water evaporation, much better than a simple mulching. Now I have this very dry and sunny spot but no flat stones here just boulders so I was thinking maybe a thick mulch would prevent the plastic from heating too much but was reluctant to give it a try. There is a reason why I never tried it yet
never needed it to heaten the soil either as it's already warm enough at planting time in my climate zone
But when I read about some of the super weird experiments some have done here I would have thought someone would have tried