Oddly enough with the rainy weather, I have been researching tarps for a primitive trip I'm planning this fall. I have some blue and brown tarps I bought from the local megastore to line my garage walls for a graduation party, but they are too thin and wimpy for wilderness use. I was surprised to learn that there is a wide variance in the thickness and weave of tarps that look alike, and are close enough in price. The local mega store sells blue tarps that are 3.5 to 5 mils in thickness. I found many sources for inexpensve tarps that were 8, 9, and even 10 mil or more. The color seems to have some relationship to the thickness, at least in the sizes and price ranges I was interested in. Blue was the thinnest, orange was 7-8 mil, forest green was 9-10 mil, and silver and white were even thicker. Tarps have fibers that criss-cross in the middle of two laminations of plastic. The more fibers per inch, the stronger the tarp. A 10x10 weave seems to be a good number to shoot for in a budget tarp. I really wanted a dark green canvas tarp, but after comparing the weight, prices, and specs, I guess I'll reluctantly go with the 9 mil forest green plastic.