I do not know enough in terms of thermal performance to give a precise opinion on this point. However, the water lost only small degree during the night (but I live in the south and the nights are mild) suggesting good efficiency. I was mainly a protection against dirt (leaves, flowers acacia ...) and here I am thrilled. I stapled the sheet along a wooden curtain rod (not the edge so it does not tear, but having made two preliminary rounds); as and as I roll the tarp above, I give a little bit of sponge ... the sheet is rigid enough not to sink in the water and so that everything does not fall to the water before having completely removed. My cheaply technique is especially useful because I have a rigid above ground swimming pool of 1m20 high.
