DCF tarp — real-world water weight retention

[cmoulder]

From time to time we read claims that one of the benefits of DCF (Cuben) tarps is that they don't absorb water — which is true — and therefore there is very little additional weight when they are packed wet — which is demonstrably incorrect.

Although DCF itself does not absorb water, it does retain water via surface tension... and the amount it can retain, even after wiping it down with a water absorbent material such as a ShamWow, can be quite a bit.

How much? Well here's my sample of one:

After a hike yesterday that featured considerable wetness, I spent the night getting rained on for several hours, safely ensconced in my HG Palace. Thankfully the rain stopped around 1-2 a.m. although there were still drops of water falling off the tree leaves for a couple of hours afterward. This morning I wiped it down with a section of ShamWow, wringing it out frequently. After wiping it down I left it up for about 1/2 hr to let the breeze help dry it some more while I made breakfast and packed all other gear.

I weighed the tarp and attached guy lines and door closure rigging when I got home. On my digital scale the total weight was 599g. When these exact same items are bone dry, the total weight is 392g, which means that even after a fairly good wipe-down this setup retained 207g (7.3oz) of water! No doubt some of the water is absorbed by the guy lines, but in the real world everything counts, and for this tarp setup this still represents a 52% weight increase.

Of course, YMMV because there are so many subjective variables, but suffice to say it's a LOT more than some folks assume.

So the next time somebody tells you the amount of water retained is minuscule... well, it ain't!!

[cmc4free]

Thanks for the write-up.

If one had the time and materials available to them, it would be an interesting experiment to compare samples (not necessarily tarps) of silnylon, silpoly, and DCF. Sample pieces of equal surface area for each material, and then results reported in % change and/or change in grams per sq foot.

Your empirical evidence is great (and practical), but the geek in me is curious for a material comparison that omits other materials such as the guylines (which as you mentioned would have contributed to the % increase, but would be the same regardless of tarp material).

Thanks for your report. Very interesting!

[cmoulder]

That is a good idea to isolate the primary materials to find out specifically, and comparatively, how much they retain.

A guy on Whiteblaze, colorado_rob, did a test a couple of years back with DCF vs Silnylon tents and got some very interesting data.

It was a bit of deja vu for me because I had made a similar discovery when using a HMG Echo II tarp made with DCF .74osy (ounce per square yd), with water retention right around 40% by weight, which I referenced somewhere in that linked thread.

Now this makes me think of another aspect... the 40% weight gain was observed with .74osy while it was over 50% with the HG Palace, which is made of .51osy material, so it might be (appears likely?!) that the thinner material retains just as much water as thicker material. So for the thinner material the amount of water represents a higher % of the total weight.

[cmc4free]

So for the thinner material the amount of water represents a higher % of the total.

That is an interesting point. But putting the geek in me away and going back to practical comparisons (what would matter to a person on the trail), you would think that a .74osy DCF and a.51osy DCF would retain the same water weight, if they had equal surface area. So while that gain in water weight would represent a higher % increase for the .51osy material, the net gain in pack weight would be the same. Right??

On the other hand, if you're looking at tarp materials on a $ per gram saved basis, then having the thinner DCF gain a higher % of its weight in retained water could be a little frustrating! I don't know the answer until I go look into it, but I'm curious if .51 DCF is cheaper than .74 DCF. It seems like it should be, even though one might consider the .51 version "higher performance" since it's lighter. They're just not necessarily suited for the same applications. EDIT: looks like comparing DCF to DCF, the cost does go up a little as the weight goes up. That makes sense from a raw material perspective, but it's almost a little surprising!

Practical considerations or "lab" experiments are probably going to lead to the same conclusions... that DCF will gain less water weight than silpoly, which will gain less water weight than silnylon.... but I still think it would be interesting to see data comparing the materials in as controlled an experiment as is practical.

I do recall reading some of that thread... I think a thread here from a while ago linked over there.

[Just Bill]

That is a good idea to isolate the primary materials to find out specifically, and comparatively, how much they retain.

A guy on Whiteblaze, colorado_rob, did a test a couple of years back with DCF vs Silnylon tents and got some very interesting data.

It was a bit of deja vu for me because I had made a similar discovery when using a HMG Echo II tarp made with DCF .74osy (ounce per square yd), with water retention right around 40% by weight, which I referenced somewhere in that linked thread.

Now this makes me think of another aspect... the 40% weight gain was observed with .74osy while it was over 50% with the HG Palace, which is made of .51osy material, so it might be (appears likely?!) that the thinner material retains just as much water as thicker material. So for the thinner material the amount of water represents a higher % of the total weight.

Your Deja Vu isn't mere voodoo...

.74 OSY x 40% = .296 (OSY of retained water)
.51 OSY x 50% = .255 (OSY of retained water)

So within reason- you basically retained the same weight per sqyd.

That jives perfectly well with the idea of retention (rather than absorption). I'm sure a DCF expert may disagree somewhat... but more or less my understanding is that the surface material is the same and it's the grid of dyneema fiber that is the weight difference. At least in these weights of DCF we are discussing.

The best description I know of regarding DCF construction- is just picture mosquito netting built from dyneema fiber with a layer of saran wrap on each side. Then heat press it and you're done.
You simply vary the weight of the mosquito netting, with the outer layer more or less a similar thickness for tarp materials. Yar- there's more to it but good enough.

That also then ties into Rob's testing of the Polycro sheet- as that literally has nothing but simple surface tension and zero chance of absorbing water.

Polycryo floor
Bone dry, 1.8 ounces
soaked/shaken, 3.0 ounces (1.2 ounces of water left) (1.2/1.8= 67%)
Wiped w/ chamois, 2.0 ounces (0.2 ounces of water left) (.2/1.8=11%)

But assuming he might have done a better job on the smaller surface area with his chamois (or lost more in the process in colorado's low humidity)... you're still in the ball park.

Unless you literally squeegee off every drop of water- you won't get it off.
Generally speaking- you probably don't want to give it an extra violent shake off either. (at least not the .51)

Overall- it is interesting (as was Rob's efforts).


I've never been totally sold on DCF (technically I've never used DCF as I wasn't sold when it was still Cuben)... but I'd like to revisit it in the future.
The general packing up issue (bulk, water retetention, avoiding creasing/wear patterns, etc.) as well as a pretty viable alternative in the .93 OSY Membrane Sil-poly has kept me away for the most part.

It seems to dry very well- so if I were to do a head to head- that's the fabric I'd try as the comparison.
https://ripstopbytheroll.com/collect...mbrane-silpoly

I haven't tried that newer .7 ish rockywoods material... that might be a good candidate as well... though I don't recall how it did with some of the BPL crowd.
I thought there were some problems with the aged HH results- but I could be wrong.
https://www.rockywoods.com/7D-Ultral...p-Nylon-Fabric

I think the other drawback... I feel a bit safer dangle drying my tarp off the back of my pack while walking with a nylon tarp.
Since the DCF is basically a plastic bag- that water isn't going anywhere until you pitch it. Maybe pure imagination- but it seems like the fabric based tarps can still evaporate off a decent bit of water if stuffed into a mesh packpanel even if you're in a spot you can't dry them a little as you go.

While DCF repairs are easy... Malto pointed out at one point that one might compare the weight of heavily patched .51 vs .74 after a thru hike as well
Even moreso when you're talking cheap *** hikers who use duct tape rather than DCF repair tape to do the patching... so perhaps a tape retention test is in order!
He told me about his attempts at .51 pants that literally wore themselves apart just from walking in them and gave up on the DCF rain pant project.

I like to push as much as the next guy... but like to find that balance point as well.
The Membrane has done pretty well for me on that front and even in the humid midwest or AT regions has seemed to dry fairly easily for me.

Having a smaller tarp for my bridges helps as well to mitigate some of the 'hit' of the heavier fabric. 7-8 sqyd vs a 11-13yard winter tarp makes that an easier call.

one of these days I'd like to do a hybrid- maybe a .51 DCF with a Membrane perimeter in my stakeless tarp. That would mean a bit better protection where you need it but lower weight where you don't.
Too many ideas- too little time, lol.

Course the TL;DR version is pretty obvious too-
If you pack up wet **** it will weigh more!

[Ohoopee]

Thank you for the observations. I remember similar results posted somewhere when
I was researching before my purchase. I had forgotten about using shammy to wipe
down the tarp though!

Thank You.

[m00ch]

That is outstanding thanks for posting those results.
One thing that is hard to graph is how much I dislike handling a wet Sil tarp compared to a wet DCF tarp.... I would say about 94% more dislike.

[SilvrSurfr]

Maybe I'm missing something. You're telling me that if my 9.1 ounce HG Winter Palace retains 50% water it will weigh 18.1 ounces until it dries out. And my 30D Silnylon Superfly, which weighs 19 ounces, will weigh 38 ounces if it also retains 50% water until it dries out?

Wow - thanks for the information. But what am I supposed to do with that information?

[cmc4free]

Maybe I'm missing something. You're telling me that if my 9.1 ounce HG Winter Palace retains 50% water it will weigh 18.1 ounces until it dries out. And my 30D Silnylon Superfly, which weighs 19 ounces, will weigh 38 ounces if it also retains 50% water until it dries out?

Wow - thanks for the information. But what am I supposed to do with that information?

Those would be 100% increases, not 50%.

[SilvrSurfr]

Those would be 100% increases, not 50%.

Sorry for the mistake. It still sounds like an "Oh, thanks for the information" moment.