Restoring silnylon (with links)

Ah, Roger, “science is the antidote to…enthusiasm.” I think we would have noticed if ePTFE let a lot of water through, too. Oh, it does, in gas but not liquid form. Just kidding, point taken, I guess we’ll see. I spent a little time searching “silicone MVTR” and didn’t get anything conclusive, nor encouraging.

Well, I found something like what I was looking for, a comparison of the MVTR (Moisture Vapor Transmission Rate) of generic silicone to generic polyurethane. Since polyurethane is the most common WPB membrane, I thought this comparison important. For what it might be worth (not a great souce, IMHO): https://blog.humiseal.com/the-importance-of-moisture-vapor-transmission-rate-of-conformal-coatings (see graph down a little ways)

Silicone slightly more permeable to water vapor than PU according to this.

science is the antidote to…enthusiasm
Hardly! Most scientists are pretty enthusiastic.
“The good thing about science is that it is true whether you believe it or not.”
(T-shirt)

Cheers

Local environmental group that advises the city council requires that for one to participate one must “believe” in science.

Chuckle.

Anyway, Roger, that was a partial quote of Adam Smith, who was probably referring to the use of enthusiasm meaning “religious fervor supposedly resulting directly from divine inspiration, typically involving speaking in tongues and wild, uncoordinated movements of the body,” which I was likening ironically to “general joy of geeking out and overthinking things.” Joke was a bit disjointed, I guess.

But back on (sub)topic, as you may have missed the above:

Well, I found something like what I was looking for, a comparison of the MVTR (Moisture Vapor Transmission Rate) of generic silicone to generic polyurethane. Since polyurethane is the most common WPB membrane material, I thought this comparison important. For what it might be worth (not a great souce, IMHO): https://blog.humiseal.com/the-importance-of-moisture-vapor-transmission-rate-of-conformal-coatings (see graph down a little ways)

Silicone slightly more permeable to water vapor than PU, according to this.

Silicone slightly more permeable to water vapor than PU, according to this.
I fully agree, based on my own observations when testing fabrics for hydrostatic head, and in particular, a fabric with silicone on one side and PU on the other. What I first observed was that applying the water pressure to the PU side gave a fabric which did have a high HH.

However, applying the water pressure to the silicone side gave a slightly unexpected result. The HH was not much different, BUT I could SEE the water getting into the fabric fibres, through the layer of silicone, and then being blocked by the PU layer (on the dry side). To be sure, the pressure was several metres water gauge in each case, but I could SEE the water creeping into the fibres, through the silicone layer.

What does this mean for a tent? Well, having the PU side of a dual-coating fabric on the outside may give you a slightly higher HH compared to having the Si layer on the outside, but I doubt this matters for a tent fly. You simply are not going to get several metres of static water pressure on your tent fly: the tent would collapse flat on the ground!

One can tape both coatings, or seam-seal them, so I question whether this matters one way or the other. (Yes, siloxane tapes ARE available.)

On the other hand, having a PU side facing downwards on the ground, for a tent floor, could well be an advantage. Under normal use you would not get several metres water gauge on the floor – unless you were kneeling on it. Hum – I had leaks through an silnylon floor once in Italy when the ground was slightly awash, but the floor was by then many years old. I recoated it in the next town with silicone sealant from the local hardware store. That worked fine.

Now, what does this mean for a jacket? Here I go slightly into pulpit mode. If you have a non-waterproof jacket you will get wet in a storm, from the rain. That’s logical.
If you have a fully waterproof jacket in a storm you will still get wet, but it will be from your own sweat. It WILL condense on the cold inside of the fabric. Pitzips never work, especially across your back with a pack there.

Me, I use a poncho with my arms inside it. See my MYOG article. Sure, some condensation, but at least I am warm. And I do not expect to stay dry.

Cheers

probably referring to the use of enthusiasm meaning “religious fervor supposedly resulting directly from divine inspiration,

Oh – like this?

Cheers