wet weight of silpoly

[Jerry Adams]

It rained over night.  I shook it out a few good shakes.  Put it in plastic bag until back home.

0.93 silpoly RSBTR

wet weight 20.8 ounces

weight after it dried thoroughly 13.8 ounces

I think that’s about the same as silnylon

[Sam Farrington]

Jerry – Another myth blasted all to heck.  Oh well.

[Jerry Adams]

maybe since the outside is silicone, it doesn’t matter whether there’s nylon or polyester inside

the shaking off of water is only affected by that silicone outer layer?

[James Marco]

I believe most [people ae interested in saturated weight, which is about 10% of an uncoated nylon. This would be worst case but add about 1.3oz to a 13oz tarp. Of course, silpoly would not have this. But, wet weight is more determined by the amount of water you shake off.

[Jerry Adams]

That makes sense.  I did shake it off fairly good but there were still a lot of small droplets.

[Dan @ Durston Gear]

If you want to decouple water soaked into the fabric, versus just on the fabric, you could somehow wet the shelter, quickly shake it off and then weigh it. Assuming the water hasn’t soaked it, the change in weight would be the weight of water on the fabric. Then repeat that but leave it to soak much longer (while continuing to apply water) and see if longer tests give you higher numbers than a quick “splash and shake”. If so, the additional weight would be saturation.

I’ve been really impressed with silpoly. The absence of sag in all night rain is amazing. Game changer IMO for trekking pole shelters that don’t have spring in the poleset to take up fabric sag. Plus you can get sil/PU poly which offers an awesome HH and also allows for seam taping, plus isn’t so slippery inside so a mat doesn’t slide around.

[Jerry Adams]

yeah, I am happy with my silpoly mid I’ve used many nights.  That is what I would choose if I made another.

[Clifford Deakyne]

I think you have just shown that the weight is water in the fabric air spaces as opposed to in the fiber.  The silicone coating must make the nylon filament as waterproof as the polyester.

It would be interesting to wet the silpoly then shake it weigh it then vacuum it with a shop vac and reweigh it.

[Jerry Adams]

or with silnylon/silpoly the silicone fills the spaces between threads, so the water is just clinging to the surface, or does silicone absorb any water?

If i spun it faster, more water would come off

maybe next time I will be more vigorous about shaking the water off and weigh that, I just shook it maybe 4 times somewhat vigorously

[James Marco]

Yes, silicone does indeed absorb water vapour. https://imageserv5.team-logic.com/mediaLibrary/99/D116_20Haibing_20Zhang_20et_20al.pdf
This study is mostly to do with gas permeability, but H20 is a rather small molecule, highly polar and is also a gas.
https://nusil.com/services/downloadmedia.ashx?mediaid=593f5a33-d7f1-46e8-a189-a337caa94fec.pdf&instantDownload=false
This quotes a .1% transmission rate for gasses through the silicone at 40C/90%RH.

Note that ultra thin coatings, such as used on Nylon6 1.1oz fabric are often stretched after curing and have higher permeability.

[Jerry Adams]

interesting, then the polyester or nylon fiber inside could absorb water even though it’s covered by silicone

[Roger Caffin]

then the polyester or nylon fiber inside could absorb water even though it’s covered by silicone
Correct imho.
I was testing fabric for HH, and with a magnifier I could see water getting into the threads on some fabric when under pressure. But only through a silicone coating, not through a PU coating, and maybe only through some silicone formulations. It did take a fair bit of pressure before the water got through to the threads.

With really good silicone coating the silicone liquid actually gets INTO the threads: that sort of coating is obviously going to be much better that one where the silicone sits mainly on the outside of the threads. That takes a high coating pressure, =$?

Cheers

[Jerry Adams]

yeah

I have silicone cookware and it seems like a different feel than silnylon.  Cookware is much harder.

[Roger Caffin]

There are probably well over 1000 different siloxane formulations. Every company has its own (and a large number).

Cheers

[Sam Farrington]

Assuming a coating with a high enough HH to keeps water from soaking into the fabric threads, the chief variable may be how hydrophobic the DWR treatment is. Fabrics all with high HH, may repel water to very differing degrees.

Working on the current tent, I wanted an inner with high water repellency, so it would shed water during pitching before the outer fly was fully attached to it. A sub one oz fabric that Extrem Textil has on sale because it is perhaps too loosely woven, surprised me because water would just not stick to it at all, so it filled the bill. Whether this ultra DWR treatment will last is an open question, but since a tent inner has a lot less exposure, it might hold up, especially if the seams are sealed and well sewn, reinforcement patches are adequate, and bonded if possible. For bonding, I’m looking at several adhesives, including the 2-part PU low viscosity adhesives that were talked about on BPL at at some length for bonding Cuben.

A number of folks have posted about satisfaction with the way Cuben sheds water and can be shaken out and packed without adding a lot of weight in water. Apparently this is a characteristic of the Mylar layers welded over the Dyneema, but any very high DWR treatment should yield the same result. We’ll see.

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