my understanding is that canvas is superior to non-breathable tent fabric in sub freezing temps because non-breathable (coated fabric) has more issues with condensation (water vapor builds up against the cold tarp/tent fabric and then condensates and freezes. i don't see any reason breathable canvas would be better for a sock than breathable dwr nylon no matter what the temps are. the only thing i see as a factor is how breathable is it? something that's minimally breathable (like goretex) would have more condensation than something that's more breathable. for instance something like goretex is technically "breathable" but the problem may be that it's not breathable enough and the water condensates and then freezes before it can pass through, so the question is HOW breathable is the fabric you plan on using? it needs to be "highly" breathable to prevent condensation/frost buildup on the inside. keep in mind that the more breathable it is, the less wind resistence it gives so you don't want it too breathable
using a tarp/sock combo shouldn't effect breathability much as the tarp IS breathable asuming it's not sealed up like a tent. if you did have a tarp that was sealed up like the superfly or whatever, you'd possibly get condensation on the underside of the tarp, but it wouldn't cause it to all of a sudden condensate inside the sock or anything, water can still pass through the sock. if it condensates on the tarp, not a real big deal, the sock should still keep you dry.
Last edited by warbonnetguy; 09-05-2012 at 13:31..