"This makes me think of Black Diamond's Epic tents. Wonder what the HH is for this?
David et al: Last year Roger tested some unused Epic Malibu for me, the earlier version fuzzy on both sides, and the later version shiny on one side. They both were dry to around 15 kPa, or very roughly 1500 mm HH, and then quickly developed many running leaks - a showerhead might be a good analogy. This was totally unlike the silnylons he tested for me, that developed some wet spots and/or transmitted a few drops somewhere between 1200-1600 mm, but continued to resist water penetration to varying degrees until the pressure became much higher. Note that I only sent Roger silnylon that, from squeeze and other primitive tests, appeared to be the most above average in water resistance.
When stretched in a circular 9" plastic embroidery loop and placed over pails on my back deck, the same Epic treated fabric survived numerous rainstorms without wetting out, until some really long storms lasting most of a day and really pouring all night.
They then became quite wet on the inside, but did not transmit measurable amounts of water into the pails. Some samples of silnylon that tested best on Roger's device, were stretched right alongside the Epic ones, and also remained dry underneath until long and heavy storms, then developed some wetted out spots and a few drops of water on the inside of the fabric and in the pails. After each rain, all the pails were dried out inside, to insure they contributed no condensation during later rains. I also think it is important that these samples were set horizontally, exposed to the full impact of vertically falling rain. To keep them from blowing away, the pails were weighed down by a brick sealed in a Ziploc bag, and the loops were held down by wooden slats that were in turn held down by bricks (not over the fabric).
After finally wetting out, and drying out, the same Epic samples were tested in further rainstorms (it rained a lot here last Fall), and along with the silnylon, behaved much the same as originally; in that they remained dry on the inside during shorter rains, but became wet on the underside after extended heavy rains. Other Epic samples were also treated with Atsko and Scotchguard silicone based sprays with no noticeably different results, except I could not tell if the sprays affected vapor permeability. I'm not sure if the Epic actually "wetted out," in the sense of being totally saturated, after these longer rains; but it made no difference for my purposes, as the wet exterior and interior would limit vapor transmission, and be uncomfortable for an occupant in a tent.
Why go to all this trouble for the Epic Malibu? Because it is a strong, quiet, drapable polyester, making an excellent tent fabric, with some elasticity but much less sagging with temperature changes than nylon; is vapor permeable even under lower vapor pressure (as in a tent wall- note the horizontal line for the Nextec on the graph in Alan Dixon's article), and will certainly resist water well for long enough to get a tent up in the pouring rain. Then, as Dan McHale suggests, it can be covered with a very light Cuben fly if the storm is expected to be prolonged.
The problem with this approach was weight. The Malibu weighs close to 1.9 osy, and with the Cuben cover added, is in the area of 2.5 osy. For me, that was too much of an increase over a single wall of 1.3-1.4 osy of silnylon, in terms of the weight difference expected for the whole tent. That, along with an unrelated consideration, the instabilty of dome tents with one pole hubbed at its ends, or two poles crossed once overhead, even with elbows to allow stiffer pole material, led me to drop the whole concept; and go back to dome designs with the poles crossed twice, and with elbows and stiffer poles as well, using a single wall of silnylon and the greatest amount of ventilation and netting between the occupant and the tent wall that I could devise. That work is still in progress.
So the length of the exposure to water pressure is an important factor perhaps not well addressed by hose and shower tests of limited duration. Another really important factor, also alluded to here, is the effect of crumpling, folding, stuffing and the like on water resistance, and is the one that gives me the most pause; but from Richard's posts, it doesn't sound like his new shelter had been used to that extent. Intuitively, flexible silicone coated nylon would be more resistant than Mylar film to such treatment; but that is only guessing. The testing protocols being developed by Roger and Richard should provide more insight about that.
Was going to comment about sensationalizing, personalizing and ridiculing; but what the heck, it's spring in North America and the sap is running. Interesting though that the sanest voice on this thread comes from Oz, where Fall is arriving. All the same, the many contributions are very helpful to my passion for tent design and much appreciated; so I don't mind the flak and yes, no denying that I said it in the earlier post, hot air. Sorry to have offended anyone.