Oct 10, 2012 at 12:06 am #1294848
It's a bit dated but Jim Wood talks about the shortcomings of silnyl dry bags (http://jwbasecamp.com/Articles/DryGear/index.html) and from a test I ran at home on a Sea2summ sil dry bag its indeed the case that when filled with water and put under moderate pressure (simulating a compressed sleeping bag pressing against surface with constant wet) it leaks.
As I know form some of richard N's tests there are many variants of HH on various fabrics – Have any of you done similar tests and can say something on the various silnyl drybags out there at this time (GG, OR, S2S etc)
Also – how do the cuben ones perform?
MikeOct 10, 2012 at 12:21 am #1919750
@hikinggrannyLocale: Gateway to Columbia River Gorge
I tried Sea to Summit silnylon dry bags in 2008 and had no problems. I duplicated Jim Wood's test: turned them inside out, filled them with water and hung them up for 20 minutes. I didn't have any of the "sweating" through the fabric pores that Jim Wood (and also a BPL review the same year, 2006 as I recall) reported. I was happy enough that I bought one for my sleeping bag and another for my insulating clothing. They proved their worth when I slipped and fell in during a dicey stream ford that summer–everything inside was bone dry although there were several inches of water inside my pack. The two dry bags still work just fine. I can only assume that Sea to Summit responded to the criticism with improvements. They do not recommend long submersion, but backpacking is not canoeing or kayaking.
On the other hand, I wouldn't trust my precious insulating gear/clothing to any "waterproof" covering without at least an annual test!Oct 10, 2012 at 1:21 am #1919754
I think that Michael and Mary are accurately describing how the same bag behaves under different conditions.
In my experience silnylon (I have some of those S2S bags but also several other types of silnylon) remains somewhat waterproof if not in prolonged contact with another surface.
So if you fill a bag and suspend it in the air it will probably not leak at all , however if you sit that on top of something else it will.
Don't know the scientific reason but you are changing the surface tension something like touching the wall of a cotton tent in the rain.
Same reason why poles under the fly can cause the fabric to leak (I had that with Epic)Oct 10, 2012 at 5:46 am #1919769
@jamesdmarcoLocale: Finger Lakes
As much as we would like to thing that silnylon is waterproof, it really isn't after even a single use. Especially for dry bags used to completly repell water, they will leak a bit. A heavier PU coating is often much better.
Pressure, vapour transfer, capilary action, dirt on the silnylon, and, surface tension can all conspire to cause some leakage, especially with "used" silnylon.Oct 10, 2012 at 5:48 am #1919770
@bowlingl25Locale: Almost Heaven
Over the summer I led a three day portage trip around Saranac Lake in NY and it rained for a better part of 24 hours. I carried my down sleeping bag and clothes in a Granite Gear Sil Nylon dry bag and was worried because it was the first time I had used it. Like I said it rained almost all day and my bag was sitting in pools of water that would build up in the canoe. However, when I got to camp and into the tent I pulled my stuff out and it had remained dry. The dry bag was never totally submerged under water but was wet/sitting in water alot of the day. So, I now believe they are reliable under most conditions.Oct 10, 2012 at 5:50 am #1919771
suspected as much….they also $$ much more
(1L GG sil was 25usd here while Exped 1L PU was 7.5USD!!!)
are the cuben drybags the ultimate solution? or do they have similar issues?
MOct 10, 2012 at 6:46 am #1919783
@retiredjerryLocale: Oregon and Washington
This isn't answering your question – which bag to buy, but
The Shield silnylon that Richard recommends is much better. My bivy bottom doesn't leak. Regular silnylon does.
Yeah, when you touch the back side of silnylon, it leaks more. Bivy bottom is probably the worst case.
I have a couple non-Shield silnylon bags. Coated them with mineral spirits/silicone. Now they don't leak.
Buy some Shield and make your own bag?Oct 10, 2012 at 7:24 am #1919795
@skopeoLocale: British Columbia
A few years ago I did a back yard test on a couple of dry bags. The idea being that if I fell in during a creek crossing, the bags would be submerged (under pressure) for a short period of time. I think it's still a valid test.Oct 10, 2012 at 8:51 am #1919823
Putting water in them and having pressure either in the form of just the weight of the water or squeezing them is more likely to cause leakage than normal use. I have used silnylon dry bags strapped onto the rack of my bicycle for a 33 day trip that involved some fairly hard rain and nothing inside got wet as far as I could tell. I did find that they were too prone to wear or other damage for that use particular use.Oct 10, 2012 at 9:04 am #1919826
I have had two silnylon taped stuff sacks leak because there is sufficient pressure against the sacks from other gear in my pack.Oct 10, 2012 at 9:49 am #1919837
I've had great luck with cuben drybags. I had a couple from Lawson and then a few MYOG ones. All of which are bonded and not sewn. Unless Zpacks has changed their methods I wouldn't recommend theirs (which are sewn).
RyanOct 10, 2012 at 5:03 pm #1920018
@scfhomeLocale: Chocorua NH, USA
It may be that added pressure at a localized point on the fabric wall expands the fabric and coating a little, while increasing the water pressure at that point, or both.
It points up a big problem with the Suter-type testers, unless they have a control for this. Roger tested some EPIC for me to around 1500 mm with a Suter-type tester; but we both know that with applied pressure, as with seam stitching and/or tent poles, it is nothing like that.
Sharp creases also have a marked effect, although I suppose you can set up a tent without sharp creases on the canopy.
Maybe we need something like a pencil eraser sticking up against the material in the Suter-type testers. Guess with the very high HH on the Thru-Hiker silnyon, not to worry. Wish Paul could get a light green or tan color that is more stealthy. The brown and dark gray will make great ultra-light tent floors, though.
Returning to the OP, the problem is that most silnylon sold today has quite low HH.
Many threads attribute this to envionmental regs, and a recent one directly to use of chemicals that affect the ozone layer. So does this mean we are being anti-green by using the stuff sold at T-H. Another conundrum.Oct 10, 2012 at 5:29 pm #1920028
This is not scientific (strictly anecdotal), but my use of silnylon bags under long term wet conditions also resulted in the fabric eventually "wetting out". No big puddles in the bag, but the stuff eventually gets moist. This has been my experience with combo pack rafting trips and what I call water hikes that involve consistent stream crossings and/or swimming. My old method of ziplock bags that were protected from abrasion by thin nylon stuff sacks worked better.
However, I've moved on to heavier dry bags in place of ziplocks (Sea to Summit "Big River" dry bags) b/c I like to hug trees. However, I'm still looking for a more reliable lightweight option. I have also had great luck for 6 months with the sea to summit "eVAC Dry bags. However, the annoying thing about the eVAC (eVENT) bags is that after a couple hours they seem to puff back up and take up a lot of space.Oct 10, 2012 at 6:27 pm #1920063
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Yeah, stock silnylon is not very waterproof.
I put my quilt in a bag made of the same shell fabric, then I put that inside a plastic bag inside a silnylon bag. The combo is still lighter than a commercial dry bag, and completely waterproof. And real cheap too!
When the plas bag dies, I replace it. But with a little care they last for months of continuous use.
Note: use a plas bag which is larger than the outer silnylon bag. put no force on the plastic.
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