I bought this in 12 x 12 in 2013. I used it over raised beds and anchored it with the bungee loops they sell. It isn't dark at all.
http://www.greenhousemegastore.com/p...th/shade-cloth
I also bought several of these in Sandstone and use daily now to protect peppers by clipping them over tomato cages when the sun gets really intense. I bought these pre 2013 and they have held up really well.
I've cut several of the 15' lengths and never had any unraveling.
http://www.greenhousemegastore.com/p...15/shade-cloth
I've also cut to cover the Aeration Screen in an EB so the mix doesn't fall into the reservoir and keep reusing the same ones after washing it off.
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One year I tried burlap and it didn't last more than a couple of months in our intense sun. In the long run, the Shade-Roll was way cheaper.