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Why no sililcone-coated WPB rainwear?
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Home › Forums › Gear Forums › Gear (General) › Why no sililcone-coated WPB rainwear?
- This topic has 9 replies, 4 voices, and was last updated 6 years, 3 months ago by Roger Caffin.
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Dec 27, 2017 at 5:30 pm #3509569
Most WPB raingear on the market relies on micro-porous or non-porous polyurethane coatings on the inner surface of the fabric to provide waterproofing, and extremely fragile and short-lived fluorocarbon “finishes” on the outer surfaces to bead up water and keep the fabric pores open so that water vapor can steam out of the garment.
Because the fluorocarbon DWRs, upon which the breathability of these fabrics rely, are so fragile and short-lived, many have switched to garments that do not rely on DWRs. As far as I can tell, these fall into two broad classes:
- Breathable but very fragile fabrics like Propore (e.g. DriDucks) and Gore-Tex Active/Shakedry that have permanently hydrophobic surfaces. These are a good solution for on-trail use but fail quickly with any rock/tree contact.
- Non-breathable and durable fabrics like silicone-coated nylon, or silnylon. These work well in well-ventilated poncho form, but are too steamy for most to wear as jackets/pants.
The dominant fabrics used for waterproof rainflies in the big brand market are coated with silicone on the outer surface and polyurethane on the inner surface. The outer layer of silicone durably beads water and the inner polyurethane layer provides durable waterproofing.
Why haven’t we seen WPB fabrics with silicone coated outer surfaces and permeable polyurethane inner membranes? This would seem to be a good solution to the WPB dilemma.
I used to think this was because silicone and polyurethane don’t “mix,” but the silicone outer/PU inner fly fabrics seem to bely this. Silnylon is not air permeable, typically, but we know from Richard Nisley’s testing that many silnylons have very low hydrostatic head but still bead water. Couldn’t an Epic-like silicone coating process, applied only to the outer face, co-exist with an inner polyurethane layer that allows moisture transport?
Dec 27, 2017 at 8:41 pm #3509584Couldn’t an Epic-like silicone coating process, applied only to the outer face, co-exist with an inner polyurethane layer that allows moisture transport?
That sounds a shade difficult to achieve. And I question the market appeal, given that the process is going to be rather expensive.Perhaps the real problem is the expectation that one can find a way to stay totally dry in pouring rain while working hard. Jest ain’t gunna happen.
Cheers
Dec 27, 2017 at 10:07 pm #3509598Roger, why would it be expensive? The silicone outer surface/PU inner surface fly fabrics are ubiquitous and cheap.
Dec 27, 2017 at 10:44 pm #3509603Yes, silnylon is cheap, but that is because the silicone polymer is applied with a doctor blade to the whole fabric span – essentially a huge scraper blade across the lot.
However, EPIC fabric is different. Every fibre is coated with a very thin layer of silicone before weaving the cloth, so that the fabric is breathable. Yes, you can blow through EPIC fabric, even if the fabric resists the passage of water. But that means the fabric is more $$. (I made my own ski jacket from EPIC Malibu fabric.)
To get an EPIC-style finish would require either a licence for the 51 patents which Nextec hold on the EPIC process or that you buy the fabric through Nextec. Then you would have to develop a coating which will stick to the silicone-encapsulated fibres. But why would you bother? You would end up with something as expensive are Goretex and with poorer performance, since the PU layer would be thicker.
Cheers
Dec 27, 2017 at 11:51 pm #3509612Why would the PU layer be thicker?
Dec 28, 2017 at 12:15 am #3509617Gore make a big thing about their Teflon layer, but in fact the WP layer on GTX is a very thin layer of PU spread across the smooth Teflon surface. Gore do NOT tell you about this in their advertising. That PU layer is why GTX fabrics also trap condensation, like any other PU-coated nylon.
To get a WP layer of PU across bare fabric requires a much thicker layer, to fill in all the gaps between the threads. If the layer was as thin as it is on smooth GTX it would have myriads of holes (between the threads) and leak.
Well known and old news.
Cheers
Dec 28, 2017 at 1:50 am #3509634OK
Dec 29, 2017 at 1:24 am #3509777If one of the questions is “could you just make a Goretex fabric with Epic Nextec as the face fabric?” I’m not sure, my suspicion is that the normal process of laminating the membrane to the face might have problems adhering to even the small amount of silicone in the fabric. Since you can find gore with nearly identical weaves on the face as Epic fabrics I assume this would be the only issue. I’m sure this could be overcome but I’m guessing the cost of development and the cost of the resulting fabric would be the ultimate barrier.
Dec 30, 2017 at 11:30 am #3509977Oh, I am sure they will come up with a solution one day. The real question is when.
Dec 30, 2017 at 11:59 am #3509978The ultimate solution is a human-sized force-field.
Could be a few years yet.Cheers
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