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  1. #1
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    pu coated vs silnylon

    sorry if this has been answered already, but what is the difference between pu coated nylon and silnylon,
    if already done please post link. (couldnt find it through search)
    thanks

  2. #2
    Joey's Avatar
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    polyurethane coated is heavier that silicon impregnated. Silnylon can "mist" through during a heavy down pour. Not much of a worry for hammock tarps, unless it's set right down on top of you.

    For comparison, check out Hennessy hammock's site, tarps. There's a Hex PU and SN tarp of same size. PU is 25 oz, SN is 19 oz.

    http://hennessyhammock.com/catalogue.html#cat

  3. #3
    Senior Member G.L.P.'s Avatar
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    I never once had a tarp made of Sil mist ....
    my DIY gravity filter is made out of Sil nylon and holds water fine
    http://en.wikipedia.org/wiki/Silnylon

    everyone had a different opinion on this .... so take as so
    i would read up on both of them and find what will work best for you

    the only time i ever seen nylon mist was in an old tent that was made out of 1.1 ripstop (not Sil)
    It puts the Underquilt on it's hammock ... It does this whenever it gets cold

  4. #4
    Joey's Avatar
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    Quote Originally Posted by G.L.P. View Post
    I never once had a tarp made of Sil mist ....
    my silnylong tarp misted during heavy rains. Glad you never experienced this...not fun. One of the reasons I don't use it anymore.

  5. #5
    Knotty's Avatar
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    With silnylon the nylon is impregnated with silicone. With polyurethane it's a coating on on the underside. PU is heavier and may peel over time. Sil is available in fewer colors/patterns and costs more. As with most things, both work, you just have to decide what's important to you.
    Knotty
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  6. #6
    Actually silnylon is silicone-coated nylon. The term "impregnated" is probably just held over from the way it was first made perhaps. Silnylon is first woven, then dyed, then coated. If you take an abrasive dish pad you can rub the coating right off your silnylon. Alot of places advertise "impregnated", but that's not really an accurate description of how it's actually made. They call it "impregnated" because everyone else does. It's basically a thin silicone coating (usually on both sides).

    silnylon is usually going to be lighter than the same fabric with a pu coating (in my exp). The pu coating will usually be waterproof at higher pressures than sil coated simply because most pu coated fabric has a much heavier coating...heavier coating=more water-resistence. Some silnylon mists through, but not all of it. i believe MLD specifically advertises that their silnylon doesn't. Since silnylon is made by multiple companies, the fabric isn't going to be identical and can vary in threadcount, weight, and water resistance.

    If you're buying a tarp from a gear manufactuer, you don't need to worry so much as they've already made sure their fabric is waterproof enough for it's intended purpose, if buying the fabric directly (from walmart for instance) it's a good idea to test it to confirm weather or not it's waterproof enough...anything with a pu coating should be while sil coated fabric can go either way as it's often straddling the line (good enough vs. not good enough)

  7. #7
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    Never had silnylon mist through, either, and I've totally swamped a tyvek tent in a downpour. (Tyvek is even more porous than silnylon, you can look up the hydrostatic head on DuPont's website if you're curious - much lower than most sil.)

    There's a huge amount of controversy about the waterproofness of sil, and a lot of debate over manufacturers and the quality being variable, etc. I just know it's kept me dry in some pretty heavy downpours. One of my tarps is made of sil seconds, the other is an OES.

  8. #8
    Knotty's Avatar
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    Very interesting warbonnettguy. I wonder if it depends on who makes it?

    The quality of silnylon is being discussed here: http://www.backpackinglight.com/cgi-...hread_id=42687
    Knotty
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  9. #9
    Senior Member ChrisH's Avatar
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    Here is a good read from the thread that Knotty linked to by member Roger Caffin on backpackinglight...hope this isn't against the rules, let me know if that is the case.

    I spent 27+ years in Textile Research with the CSIRO, ending up as a Senior Principal Research Scientist with a large team under me.
    I have a Suter tester (it measures the pressure rating of a fabric) of my own and I have been testing (on my own behalf) light-weight coated fabrics for many years (6+).
    I have tested many of the fabrics from the various suppliers in the American cottage industry - (thanks to various people including Sam for all the samples).
    I keep seeing claims of 'our silnylon is superior', but I have yet to find a sample that really is superior. Some show normal variation; others are actually inferior.

    I have tested Asian fabrics which are nylon 6.6, have a pressure rating several times that of the stock American silnylon, and are slightly lighter than stock silnylon. (Also polyesters.) Some of those fabrics have pressure rating of up to 80 kPa, compared to stock Westmark silnylon which is around 15 kPa.

    The old 'wet-look' Westmark silnylon also got to 80 kPa, but the coating company (Duro) had its coating line closed down by the EPA because it was releasing too much solvent into the atmosphere. They could not be bothered upgrading their plant. As noted by some, operations in Asia are not restricted by the EPA.

    The current Skylite silnylon from Westmark is not designed for our outdoors use. It is designed for parachutes and for the huge blow-up advertising puppets you see outside (or on top of) shopping centres. Neither of those markets have a water-pressure requirement. Unfortunately Westmark does not feel enough market pressure to improve the pressure rating - perhaps because those outdoors companies which are concerned have simply gone to Asia for their fabrics.

    Some people have claimed that Asian fabrics are inferior. Nice try guys, but no cookie. Some (most?) of the world's major high-tech textile companies are located in Asia. You have only to ask what happened to Pertex: the UK holding company sold the brand and tech knowledge to Mitsui.

    Now for some technical details. Please note that every statement made here is one based on actual measurement or observation. No guessing at all.

    You might like to note that 10 kPa is roughly equivalent to 1 m (1000 mm) water pressure. I tend to work in kPa.

    I will have to take some photos of pressure testing. A fabric with 20 kPa pressure across it is bulging quite significantly. When the fabric gets to 80 kPa (8000 mm) presure the bulge is ... startling. Or alarming.

    The idea that a tent fly (tarp, whatever) will experience broad pressures of 15 - 20 kPa from rain is mostly unreal (typhoons excepted!) imho. The tent would explode from the ground due to the forces involved. And you won't get spot pressures on a fly like that either: the existing surface film of water dissipates the impact of every (non-typhoon) rain drop very well. Water flows; bullets don't.

    However, you can easily get 60 kPa on a groundsheet when you kneel on it. That's where the problem really arises. That is why so many companies use a heavier fabric for the groundsheet: they don't want customers getting wet knees. Customers don't want wet knees either ...

    Misting
    I understand that some people like to blame their tent for their getting wet inside. But just wanting to blame someone else is not a substitute for proper testing and decent science. So-called 'misting' is condensation being popped off the inside of the tent due to the impact of raindrops. (There is one exception I will come to later.)

    Why should one get condensation on the inside of a fly/tarp/whatever when it is raining? The reasons are a shade complex, but the effect is at least partly driven by the way the temperature of the fabric is lowered by the cooling effect of the rain. You get a wet outer surface and the water on the outside starts to evaporate a bit, cooling the fabric. Ever seen your windscreen fog up inside when it is raining outside? Same effect. So you turn on the heating a bit and warm up the windscreen.

    On the inside of the tent you have a person who is warm, possibly with damp clothing, and the ground is wet, all evaporating away. That makes the inside of the tent around 100% RH, but at a slightly warmer temperature than the ambient, and even warmer than the fabric. When that warm saturated air hits the colder fabric, condensation happens. Yes, this can happen even with some ventilation due to a breeze: the breeze may just be cooling the fabric down even more by evaporation.

    For the doubters - note that you can get condensation even when it is not raining, like under a clear sky. The fabric is cooling down here because it is losing heat to the night sky by radiation. The night sky can look as low as -70 C (-94 F). You don't need many degrees of temperature drop for condensation to happen.

    Yes, there is one exception, and that is EPIC fabric. This is funny stuff. It has air-flow but blocks water - up to an abrupt threshold. That threshold is set by the surface tension of the water on the coating on the fibres, and is around 15 kPa for clean new fabric. BUT, get dirt, skin oils, vegetable oils, or anything else, on the fabric, and the surface tension effect is shot to pieces. Then the fabric starts to leak like an uncoated fabric - at essentially zero pressure. So your nice new EPIC tent is waterproof for a few days, then collapses.

    Where do we go from here?

    It seems that the silicone coating is porous under pressure. I am not talking about a few leaky spots here and there. I mean the silicone polymer seems to be actually micro-porous. Under pressure the threads inside the fabric start to get wet. I have watched this happen during testing. However, when I test a fabric with a PU coating on one side and a silicone coating on the other, I see thread-wetting from the silicone side but not from the PU side. Yes, that means the PU coating is inherently more pressure-resistant.

    The old PU coatings which sat on the surface rather than going into the fabric actually weakened the fabric, while the silicone coating/impregantion does strengthen the fabric. However, we now have PU coatings which go into the fabric the same way as the silicone coatings do. I expect these to strengthen the fabric.

    So I am currently betting on the future being fabrics with a silicone/PU coating - either as a copolymer or as a different coating on each side. And they will be coming from Asia, as so far the American suppliers show no sign of competing.

  10. #10
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    Quote Originally Posted by lori View Post
    Never had silnylon mist through, either, and I've totally swamped a tyvek tent in a downpour. (Tyvek is even more porous than silnylon, you can look up the hydrostatic head on DuPont's website if you're curious - much lower than most sil.)

    There's a huge amount of controversy about the waterproofness of sil, and a lot of debate over manufacturers and the quality being variable, etc. I just know it's kept me dry in some pretty heavy downpours. One of my tarps is made of sil seconds, the other is an OES.

    Lori, Tyvek is breathable roofing membrane so will always let a significant amount of water through, since that's what its designed to do when its acting as a roof membrane underneath slate/tile/shingle etc.

    I see Tyvek being talked about on here a lot as a mat to use under a tarp and various other uses. It's actually pretty poor for anything apart from its intended use so it surprises me when I see people talking about it.

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