Ahh, got it. Just never thought of using a hydrostatic test to describe the material. I'm used to using them for other things. Makes a lot more sense now. Thanks! I wonder if it would really hold off 1.5 meters worth of water at 8.3lbs per gallon but if I'm in that kind of a storm I'm more interested in looking for an Ark than worrying about my tent! <grin>