Since camping season’s coming up soon for me. A question that’s always been on my mind is “Why can’t one touch the tent in the rain or dew?” I know it’s prone to leak where it’s been touched, but why?
WAG: most tents are made of synthetics like Nylon. Condensation forms on the outer surface when rain falls or dew settles. When you touch the inside of the tent, the fabric is porous, so the liquid seeps through to the inside and now the condensation starts falling on your sleeping bag. And nobody likes waking up damp, or worse, soaking wet. I think of it as a “wicking” action. (think candle wick)
I find a good water repellent tarp over the whole thing avoids this mess, along with a good seam sealer on the tent seams.
Once I was camping with the family and dad brough two teeny pup tents for my sister and I, but no tarps to cover the top. We tossed old wool army blankets on top of the tents. Soaked up the moisture, so it didn’t soak through to us.
Another WAG, but I always thought it had to do something with the breaking the surface tension of the water on a tent with a relatively loose weave. On the newer waterproof tents, this isn’t really a problem.
I was told by my scout leaders years ago that touching the tent while it was wet caused the water-repellant coating to come off in that spot.
A single-wall tent cannot be made waterproof, or you’d get lots of moisture inside from the condensation of your breath and insensible perspiration. The water repellent fabrics used will allow water vapor to pass out, and while they generally keep liquid on the outside, anything touching on the inside provides a path for it. I would guess the mechanism is most likely what [brjciii]** suggested, disturbing surface tension.
Tents with flies (a separate roof, so to speak) use breathable fabric on the walls for superior dispersal of internal moisture, protected by a waterproof covering equivalent to, but much more elegant than, the tarp mentioned by Dogzilla. On those designs, touching the inside walls does not bring leakage in.