The persistent DCF water weight myth

[MikekiM]

Weighing the wet guy lines doesn't sound particularly wise. That tells us nothing about whether it's the guy lines absorbing the water or the DCF tarp itself.

Nevertheless, it's reassuring to see that a DCF tarp will ALWAYS weigh less than silpoly or silnylon, wet or not.

Absolutely agree... I don't know enough about the science of DCF.. but I do know that regardless of how well I wiped and shook, I still carried nearly 10 oz of water weight somewhere in that rig.

My comment was more observation than science..

[cmoulder]

I'm not going to remove my guy lines, but I happen to have a hank of Glowire that I can weigh dry and wet.

All for science.

[FLTurtle]

Surface tension is weird. I would imagine that wiping/shaking will leave behind some microscopic water beads, but 8 oz worth? The square footage of an 11' hex would be about 80 sqft, double since you got the inside and outside surfaces. I would hope the inside of the tarp is dry, unless condensation and morning dew? I guess it's possible to spread out that much water and still appear to be dry. If 8 oz was evenly distributed on both sides you're only talking a half ounce (1 tablespoon) per 10 sq ft.

I don't have a DCF tarp, but are they PU coated?

[cmoulder]

Surface tension is weird. I would imagine that wiping/shaking will leave behind some microscopic water beads, but 8 oz worth? The square footage of an 11' hex would be about 80 sqft, double since you got the inside and outside surfaces. I would hope the inside of the tarp is dry, unless condensation and morning dew? I guess it's possible to spread out that much water and still appear to be dry. If 8 oz was evenly distributed on both sides you're only talking a half ounce (1 tablespoon) per 10 sq ft.

I don't have a DCF tarp, but are they PU coated?

Yes, it's hard to believe that 'mere' surface tension could retain so much water. Many people are surprised to learn it can be so much.

DCF is made of very thin Dyneema fibers sandwiched between layers of Mylar (plastic).

I weighed a dry 50' hank of Glowire... 59.6g. Soaked it in water for 10 minutes, shook out 'til it didn't drip, but still quite damp as Guy/Ridge lines would be on the tarp... 74.5g. So 14.9g water retained... a little over 1/2oz in weight.

[cmc4free]

Yes, it's hard to believe that 'mere' surface tension could retain so much water. Many people are surprised to learn it can be so much.

DCF is made of very thin Dyneema fibers sandwiched between layers of Mylar (plastic).

I weighed a dry 50' hank of Glowire... 59.6g. Soaked it in water for 10 minutes, shook out 'til it didn't drip, but still quite damp as Guy/Ridge lines would be on the tarp... 74.5g. So 14.9g water retained... a little over 1/2oz in weight.

Interesting. I had no doubt the tarp would retain more water than the guylines, but I didn't expect the difference to be that drastic. Using your dry/wet Glowire numbers and comparing with your full tarp system numbers, the guylines only account for .53 oz or just under 8% of the total added water weight you measured. Even if someone used UHMWPE cordage, which might retain a little less water than Glowire (or maybe not due to the hollow core and capillary action), the difference would be negligible and greatly outweighed by the water retained by the tarp.

I'd guess 3 tarps of the same square footage ranked by water retention would line up like this:

- DCF (least water retention)
- Silpoly
- Silnylon (most water retention)

Therefore the heaviest tarp at the start would gain the most added water weight and the lightest tarp at the start would gain the least - so this is still good for news for DCF being the UL champ. But I also understand your point was to (once again) empirically dispel the myth that DCF "absorbs" no water, etc.

Thanks for your data. Interesting, as usual.

[cmc4free]

One thing I have never tested is drying time, but my impression — and somebody might be able to correct me on this — is that DCF does indeed dry out quicker in identical conditions compared to silpoly or silnylon.

This seems a reasonable assumption given that a new DCF tarp will have unbroken layers of mylar on either side of the weave, whereas a silpoly or silnylon tarp has exposed weave (unless it has PU coating). The moisture on DCF will be almost purely held by surface tension, compared to more absorption with silnylon/poly, so I would expect the DCF to dry much faster. Lacking any empirical data, I'll add that a DCF tarp dries in my dark, sealed garaged within an hour or two, while a sil tarp will take up to a day to dry completely in the same conditions.

[Brooklyn]

This seems a reasonable assumption given that a new DCF tarp will have unbroken layers of mylar on either side of the weave, whereas a silpoly or silnylon tarp has exposed weave (unless it has PU coating). The moisture on DCF will be almost purely held by surface tension, compared to more absorption with silnylon/poly, so I would expect the DCF to dry much faster. Lacking any empirical data, I'll add that a DCF tarp dries in my dark, sealed garaged within an hour or two, while a sil tarp will take up to a day to dry completely in the same conditions.

^__ this is the explanation I most agree with here. Plastic doesn’t absorb water. Water hangs around via surface tension, but a silnylon/poly will absorb water and weigh more after being rained on than the already much lighter DCF.

Think about it this way, a rain jacket with enough rain will wet out. A plastic bag will not. The plastic bag will weigh more than it did dry because, you know, science.

[TallPaul]

Back to the original post... are we saying DCF doesn’t absorb water but will retain it via surface tension? Whereas other fabrics will likely absorb and retain via surface tension?

I’m probably slow in getting that nuance from the post.

[michigandave]

Back to the original post... are we saying DCF doesn’t absorb water but will retain it via surface tension? Whereas other fabrics will likely absorb and retain via surface tension?

I’m probably slow in getting that nuance from the post.

That's how I'm understanding it. The DCF is heavier when water is still on the surface. To me, it all makes sense. If I put my DCF tarp in the DCF bag after taking it down after a rain, there will be residual water in the bag.

In the big picture, we're only talking about a few ounces or so of water. Non issue to me and it is what it is.

[fallkniven]

Back to the original post... are we saying DCF doesn’t absorb water but will retain it via surface tension? Whereas other fabrics will likely absorb and retain via surface tension?

I’m probably slow in getting that nuance from the post.

Yes, dcf does not absorb any moisture, all this thread is talking about is the weight of the water remained on the surface. I'm surprised as much as it is, but either way its a heck of a lot better than my old silnylon sponge I mean tarp.