- Jan 16, 2015 at 8:11 pm #1324651
It sounds from your posts that you are quite knowledgeable about Epic treatments. The Epic Malibu formerly used by Black Diamond was one of the very few WPB materials that would function at low enough humidity to be used to effectively deter condensation for a shelter wall. Black Diamond has had a newer material for some time, but reports suggest that it is not anywhere near as durable as the Malibu.
The issues with Malibu were its weight, close to 2 oz/yd2, and judging from tests done by Roger Caffin and others, it tended to fail badly over 1500mm HH, in that water comes through in large amounts. Some silnylons that test only to about the same point, at higher pressure allow only a few drops to pass through, up to various levels above 3000mm, where they fail badly also.
Also, I have found that some fabrics that test well for HH, if left in a stormy environment for several weeks will eventually lose water resistance and allow water to penetrate, creating a wet inner wall. So extended testing is required to fully ascertain the usefulness of a fabric for a shelter wall in areas where rain can be extended.
However, functional WPB fabric for a SUL shelter remains the golden fleece for tents. At least for those like me whose desire was whetted by the Malibu. So I'm interested in your views about the feasibility of WPB shelter fabric in the 1 oz/yd2 range. For example, GoLite had a material around 1.1oz/yd2 that it used for its Poncho Tarp that was supposed to be WPB at 1200mm HH, and a number of people reported luck with using it as a low tarp and experiencing minimal condensation. Others have used the 'Impetus' material for tarps, including one manufacturer; but after exposing it to extended rain, I'm doubtful whether it is water resistant enough for tents. Also, there was a link posted recently to a snippet about GTX' attempts to develop a WPB tent fabric, but it sounds as if in the early stages, and much remains to be worked out.
Are we chasing rainbows here, or is there some potential for an almost condensation free SUL single wall tent. I'd be very interested in yours and others' thoughts on this subject. Thanks.Jan 17, 2015 at 3:46 pm #2165563Paul McLaughlinBPL Member
IIRC, the actual Gore-tex membrane by itself, with no face or lining fabric, weighs about .5 oz/yd.
The lightest Event I've seen (which I believe was a special fabric run for BPL)is about 2.25 oz/yd. Face fabric is ripstop and I'd guess it must be around 1 oz/yd; lining is very open weave tricot and might be under an ounce – almost has to be unless the Event membrane is significantly lighter than Gore's.
A typical minimum effective coating weight is around .3 oz/yd or so, judging from Silnylon and some other light coated fabrics.
Assuming a three-layer fabric, if the face is .67 (as in Argon) and the membrane could be .4, and the lining could be something like nanoseeum at.6, then you'd end up with around 1.7 – or more likely more since there has to be adhesive in there somewhere. From what I understand that was the weight of the EPIC Malibu that BD used, but I don't have solid info in that.
Having used a BD EPIC tent I found it did okay on condensation but it wasn't free of it (I don't think any tent is). And the general consensus on those tents was that some of them shed rain well and others didn't – apparently there was considerable variation in the fabric's performance.
Given that there currently isn't ANY fabric at ANY weight that is the real deal holy grail (though maybe the fuzzy interior Toddtex comes closest) I rather doubt we're going to see an ultralight fabric that comes close to the performance you seek. That said, something Cuben-ish could prove me wrong.Jan 17, 2015 at 6:21 pm #2165601
I didn't mention Propore due to its fragility in very light weight, but were that not the case, it might work very well. The heavier propore, mentioned in a recent thread here on bivies, is extremely vapor permeable, but again, too heavy for an SUL tent.
Not sure eVent would be sufficiently vapor permeable for a dry tent wall. Nearly all the WPBs that work OK in attire, require more pressure from humidity in order to work than would often be the case with a tent wall. The graph in Alan Dixon's article ranks the offerings quite well:
Note Alan's observation: "Propore breathes equally well at low and high humidity levels. Propore is another extremely breathable fabric with DMPC water vapor transmission rates (breathability) that exceed Gore-Tex XCR."
A very light Propore, bonded somehow to a ten denier woven nylon or polyester with high quality DWR on the outside might do it. So I'm more optimistic.
BTW, 1.7 oz/yd2 was the weight often given for Epic Malibu, but in its time, I bought remnants from a number of different sources, and it always ran between 1.8 and 1.9 oz/yd2. The variation is not surprising, given the inconsistencies in manufacture that you mention. But since the Black Diamond tents had to be carefully seam sealed with silicone, not urethane sealer, I always wondered if a lot of folks just didn't bother to, used the wrong sealer, or didn't seal well. After reading hundreds of threads on this and other forums, I never found one where the unhappy (and wet) BD tent user specified careful sealing with the right sealer.
Your comment suggesting significant moisture from condensation on the inner walls of your BD tent is interesting. I hadn't seen that before, or maybe the mind just grew fuzzy after reading hours of threads.Jan 18, 2015 at 7:49 am #2165704kevin timmBPL Member
@ktimmLocale: Colorado (SeekOutside)
But you simply get much better performance with a double wall system. A 1.4 ounce 30D and a 1.1 DWR is 2.5 ounces, and cures almost all condensation. The downside, is more material and construction costs.Jan 18, 2015 at 8:10 am #2165713AnonymousInactive
.Jan 18, 2015 at 1:59 pm #2165794
Re: A 1.4 ounce 30D and a 1.1 DWR is 2.5 ounces, and cures almost all condensation.
The condensation is still there, you just can't see it.
Double wall has a point for winter tents, but why drag around the weight in the other three seasons.
You can get a good 1.1 oz/yd2 coated material now by cannibalizing tarps, but as the HH goes up, so does the price. And you're still going to be adding around 0.7 oz/yd2 or more for an inner that will allow vapor to escape to the outer. That's 1.8 oz/yd2 total for the two layers of canopy. That's about the same as Epic Malibu, and I would choose that instead if the weight were acceptable, due to its strength, elasticity, lack of sag with the polyester, and ease and strength of construction with strong sewn seams. But for me, that weight is not acceptable for SUL BP, and a lighter alternative is needed with a material that has the advantages of a woven fabric. Anyone have any ideas?Jan 18, 2015 at 2:04 pm #2165795
Re: Two thin layers of say a very tightly woven, smaller fibered (but not microfiber sized) polypropylene material on top of each other should theoretically give enough air porosity and be water resistant enough for most conditions, all while being lighter weight and fairly durable and strong.
You say theoretically, but do you have any examples of anything to support that.Jan 18, 2015 at 6:43 pm #2165873AnonymousInactive
.Jan 30, 2015 at 6:57 pm #2169915
Was just about to give up on this when this post came up on the GEAR forum:
The current WPB Cuben from Zpacks is around 1.6 oz/yd2 and produces a jacket weighing around 5.5 oz. Richard's tests for the breathability were not too encouraging, however.
So if the jacket using the new material is 4 oz as stated on the thread, the material weight might well be under !.5 oz/yd2, and the claimed breathability is outstanding.
Possibly a great choice for a single wall tent canopy with no netting except at doors and vents.
But is it really, or just more marketing at work. Which raises the perennial question: Should I stay or should I sew?Jan 30, 2015 at 10:19 pm #2169974Paul McLaughlinBPL Member
Here's the other thing to consider: condensation isn't simply a matter of breathability. You can get condensation on a very breathable fabric – one so breathable that it makes a poor windshell – simply due to the effect of moist air contacting a cold surface. Dew point is a tricky thing because it changes with both temperature and humidity. When you in your shelter raise the humidity (as you always do, both by respiration and by perspiration whether sensible or insensible), if the change in humidity brings the environment close to the dewpoint, then the tent wall, which is commonly a little colder than the interior air, may be just cold enough to cause condensation as the moist air contacts it – regardless of the breathability of the fabric. A double wall tent combats this simply by being a double wall; the inner fabric is just a little warmer than the outer, and that difference may be all it takes to avoid condensation. And yes, you may still get condensation on the outer ( though that should be less as the outer ought to be better ventilated than the inner) but that condensation is where you won't touch it from the inside.
My personal experience has been that there is no such thing as a condensation -free shelter; some conditions are just too harsh. And the variations of fabric and single or double wall each have conditions where they shine. I've used gore-tex tents both MYOG and manufactured, single wall coated floorless shelters, and conventional double wall tents, and of course tarps. I've had condensation in all of them, and been without condensation in all, under varying conditions.
My general take is that for dry cold situations the single-wall W/B tents work pretty darn well – the beauty part being that if you cook inside and heat up the interior you create conditions where the fabric is at its best – a large gradient in both temperature and humidity between inside and out, and the fabric is kept pretty warm, so an amazing amount of moisture can pass through. Try that in a single-wall coated shelter and it's a steambath and water is running down the walls. Even a double-wall can't handle that situation as well as the W/B. On the other hand, in cold, humid, rainy situations (or wet snow) the single wall w/b is at it's worst in terms of breathability, particularly if the face fabric wets out due to aged DWR. In that situation give me a double wall all the way – there will be condensation on the fly for sure but the inner tent will be drier than the inside of the W/B tent – and warmer to boot.
For me the one thing that a W/B shelter can do that nothing else can would be to function as both bivy sack and shelter depending on whether you put in the poles. thus, you could just lay it out and use it as a bivy sack – but then if something comes up in the night you can zip yourself in and you're covered – and if the poles can be erected from inside (as in a BD firstlight or a Bibler) then you can tentify if you choose without getting out in the weather. Might be nice.Jan 31, 2015 at 7:16 pm #2170165
Thank you for those observations. They make an awfully good argument in favor of double wall tents, even if limited to 3 season use (which in the mountains can become 4 season unexpectedly).
Your point about potential for condensation, even on highly breathable material, is appreciated. I've also noted that in experimenting with canopies in heavy rain that the condensation can be high regardless of whether the enclosure is occupied.
My tenting experience is a little different, because I no longer enjoy camping in freezing weather, except for dips in temperature during the night. So it is the cold, humid and rainy situations you mention that are the greatest concern. When trekking above timberline, such weather, along with high winds, can threaten hypothermia, and the last thing needed is an enclosure that is soaking wet on the inside.
In such circumstances, I've found that net inners that do not touch the outer wall have protected me fully from condensation, and provided a dry place to warm up, even though there is condensation on the inside of the outer wall. In the quest for lighter weight, I don't want to give up that kind of protection.
So I've come around to designing side entry tents with zipped netting that covers both of the long walls under the vestibules (not original – TarpTent Rainbow); and on the narrow end walls, with strips of netting under the canopy to vent along the tops of the floor walls. The floor being silnylon, is pulled tightly taut from all corners so it will not slide around over the ground.
In addition, I'm thinking about placing 17 gm/m2 netting with Velcro attachments over the lower portions of the head and foot areas. Unlike the net doors and end vents, this netting would not be load bearing, so could be very light weight, and easily replaceable with the Velcro.
That would still leave the tent wall ceiling at the head and foot ends above shoulder height when sitting without any protection from condensation. So there will be several top vents also to try to limit that. If that doesn't work well, there will be some Velcro tabs sewn in place where needed to raise the netting to a higher level. Unfortunately, the potential for the added netting limits inside space, so the canopy will have to be bit larger, which adds a little weight, but not much.
Concerns are often voiced about net inners that heavy condensation will drip from the outer ceiling through the netting. With good venting, I've not had that problem.
If we are wrong, and a proven, very light weight condensation free single wall material can be found, that would seem the obvious choice. In the meantime, the above is about the best I've come up with in the effort to achieve reduced weight without greater exposure to condensation.
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