I purchased the XL size. Not to par with my expectations after reading reviews. Areas where the 2 pieces overlapped appear considerably more effective in blocking out the sun (Overlap covered two thirds of my windscreen). The issue is where there was no overlap I could feel warmth and see some light coming through as opposed to overlapping areas which were completely dark without any warmth. Based on this I feel the material is thinner and feels flimsier than what I was expecting but still does an adequate job overall.
I like the versatility in having 2 pieces which allows full coverage of windscreen. As opposed to 1 piece units which tend to be too small or troublesome to fit.