In testing the effect of heat on suspended Cuben with a heat gun, found that it did not cause the material to shrink - just the opposite, in fact. It expanded and sagged a little. Also, all of the many little wrinkles or multiple creases that appear on Cuben in use sort of melted out of existence.
This was not heat intensive enough to be intended to melt the material, however. The outer surface is a plastic, and I'd be very surprised if it would not melt, and eventually ignite at some point with continued exposure to flame or high heat. The inner, or sandwiched material, dyneema or spectra, is a thermoplastic that I would also expect to melt; not to be confused with aramid fibers, like Kevlar, that go into highly fire-resistance materials like Nomex.
Will not be trying to ignite or melt Cuben, because can see no need or useful info from that. It is no more flammable than silnylon, probably less, so no new problems presented. Thanks, John, for the helpful info you assembled and presented.
Unless, of course, this is really about the winter tent thing on the current related thread. Would love to be a fly on the wall in the room where some of these threads get cooked up. Could not do it now, though, because have given up drinking for Advent, and would need some form of artificial stimulant to keep my sense of humor.