Is Non-Coated Material Warmer Then Coated When Using an UQ

Is a non-coated fabric warmer than a coated fabric for use in hammock bodies when using an underquilt?

My thought is this, the more breathable the fabric is the more warm air will pass between you and the underquilt. A non-coated ripstop will allow more air travel than DWR. When I am laying in my non-coated or taffeta hammock, I can feel the air hitting my a lot more than in my HH.

My reasoning is this. Last winter I did some cold weather day hiking. Most of the time I was hiking in my smartwool midweights and rain jacket. When I stopped I put my insulated jacket on. I was noticable warmer when I had the layers me, smartwool shirt, insulated jacket, than rain jacket vs me smartwool shirt, rain jacket, than insulated jacket.

This is basically keeping the windbreaking layer on the outside of the setup instead of somewhere in the middle. This could apply to a hammock insulation.

I was talking to BB on this. He brought up a couple good points. A non-coated fabric will allow more convective heat transfer between you and the underquilt. With a coated fabric you are getting most of your heat through diffusion and only some through convection. Over time both fabrics would result in the same or similar amounts of warmth. The biggest difference would be in the non-coated fabric allowing the user to heat up faster. Something important in cold weather or on short hanging breaks.

And yes I realize this is arguing the top of the pyrimad so to speak. The engineer in me is trying to get the most out of what I am using.

Two extremes - vapor barrier vs net hammock. Vapor barrier is warmer. Take it down a notch - DWR coated vs regular ripstop. Same principle, just not as extreme.

The best way to stay warm is to minimize ALL heat transfer...since it's always transfered FROM you TO the underquilt and beyond, you're losing heat. The reason underquilts are warm is b/c the microclimes in each little down cluster are poor conductors...so they trap the heat instead of letting it out to the environment. But at the beginning, it still took that heat from your body. Whether it's conduction or convection, that's bad...so minimizing all heat transfer (in this case, especially convection) would keep you warmer. Until the condensation starts, at least...but even that's ok w/o ventilation (convection and evaporation) b/c it's a vapor barrier.

So IMO DWR coated fabrics would be warmer.

But like you said, it doesn't really make much difference...the underquilt is providing the windbreak, just as your jacket did. So as long as the wind doesn't get between your hammock and underquilt, and short of a vapor barrier hammock, it doesn't make much difference.

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Originally Posted by Just Jeff

Two extremes - vapor barrier vs net hammock. Vapor barrier is warmer. Take it down a notch - DWR coated vs regular ripstop. Same principle, just not as extreme.

The best way to stay warm is to minimize ALL heat transfer...since it's always transfered FROM you TO the underquilt and beyond, you're losing heat. The reason underquilts are warm is b/c the microclimes in each little down cluster are poor conductors...so they trap the heat instead of letting it out to the environment. But at the beginning, it still took that heat from your body. Whether it's conduction or convection, that's bad...so minimizing all heat transfer (in this case, especially convection) would keep you warmer. Until the condensation starts, at least...but even that's ok w/o ventilation (convection and evaporation) b/c it's a vapor barrier.

So IMO DWR coated fabrics would be warmer.

But like you said, it doesn't really make much difference...the underquilt is providing the windbreak, just as your jacket did. So as long as the wind doesn't get between your hammock and underquilt, and short of a vapor barrier hammock, it doesn't make much difference.

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Here's my take on the issue, in case anyone cares :p

Temperature ratings measure the range of outside temperatures under which an insulated system (user + quilt) can be considered closed. That is, negligible heat loss to the outside. Obviously this is an important consideration. And since convective heat transfer is generally the predominating method of transfer in most systems of this type, less air movement means better insulation. This is the advantage of using DWR or other less-than-breathable fabrics for quilt shells.

On the other hand, the "warm-up time" is an important factor too. Before the user enters the system, the air inside the quilt is in near-equilibrium with the outside air - it's cold. When the user enters, there's a transient period before the air forms the proper temperature gradient: user-temp on the inside, outside temp on the outside. Until the air near the inner shell is in equilibrium with the user, the user will continue to feel cold due to heat loss. The time it takes for this to happen can be critical in cold situations.

Allowing more convective heat transfer at the inner shell would reduce the "warm-up time". Especially since convection is much quicker than diffusion. So using an untreated (more breathable) inner shell would be a solution to this problem. On the other hand, allowing more breathability would also make the quilt less insulative overall. Therein lies the tradeoff. However, I think that the reduction in overall insulation value would be quite small, considering that the outer shell would still be convection-resistant and that the insulation itself is designed to reduce air flow.

In other words, I think theory supports a more effective overall system that uses a very breathable inner shell (untreated ripstop) and a less-breathable outer shell (DWR). There are other considerations, though - for instance, DWR is desirable for both shells because it helps keep the insulation dry.

I've actually tested the "warm-up time" theory - the prototype quilt I've been using for some time now has an untreated inner shell. It definitely gets warm quicker than the underquilt I'm borrowing from Jeff, which is DWR top and bottom.

Two points:

1 - Heat transfer from your body to the quilt is mostly conductive since it's touching...convective between your body and the insulation is negligible.

2 - Basic assumption that it's a closed system is false. Your body is always losing heat to the outside, even inside the quilt. Thicker insulation just slows the transfer enough that your body can produce heat at the same or greater rate as it's lost. So again...anything that slows heat transfer is better.

Personally, I think the untreated stuff is just more comfortable so I use it for my hammocks...at least for the $1 bin stuff I use. If I thought it would make a real difference in warmth I might switch to DWR.

I'm even half considering making a silnylon hammock just to see what it really feels like...I've heard a few other folks say it's not so bad, and the Crazy Creek I tested didn't give me condensation problems. Making an insulated hammock w/ sil as the body and DWR as the shell should help with moisture inside the insulation, too. 'Cept all of the sil I have at the moment is 1.1 oz.

Moisture is the enemy....it robs heat faster than air once it becomes liquid... non breathable material will loose any heat retention advantage when the moisture build up negatives are factored ....

pan

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Originally Posted by Just Jeff

1 - Heat transfer from your body to the quilt is mostly conductive since it's touching...convective between your body and the insulation is negligible.

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Most places, your body isn't actually touching the quilt - there's air space in between. Heat flow into the quilt is primarily conductive IF you're using a low-breathability shell material. That was my point - convection is much faster, so to heat the insulation more quickly you would want a breathable inner shell.

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Originally Posted by Just Jeff

2 - Basic assumption that it's a closed system is false. Your body is always losing heat to the outside, even inside the quilt. Thicker insulation just slows the transfer enough that your body can produce heat at the same or greater rate as it's lost. So again...anything that slows heat transfer is better.

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Heat flow in = heat flow out ==> closed system approximation.

The quality of the discussion can always be indicated by the heavy hitting contributors. 4 for 4 on this one...

A good thread to pay attention to IMO, although I do not have the experience to add anything.. yet... :)

Keep up the good work guys!

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Originally Posted by blackbishop351

Heat flow in = heat flow out ==> closed system approximation.

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Oh - I see what you mean. I was thinking in terms of the material - the loft plays a bigger role in transfer rate than the material, so it's only a closed system b/c the loft makes it so. But given that the loft makes it so, for the purposes of choosing the material you could say it approximates a closed system. Fair enough. (Was that a roundabout way of saying "I gotcha" or what?)

But if there's air between the hammock and quilt, you're using it wrong. My quilt touches my hammock, and my hammock touches my clothes, and my clothes touch my body - with VERY little air in between - so the heat transfer is primarily conductive (especially in my DownHammock).

Hrm...that brings up another question. What's the transfer mechanism for heat from one down cluster to another as it moves through the underquilt? Convection, b/c each cluster makes a microclime and the heat has to travel between the microclimes? A little bit of conduction obviously. And radiation? Probably even some evaporation in there...but what's the primary means? Is the convection more than the radiation?

Thinking so hard just made my eyebrows start hurting. Need to check out the new two-person hammock I just built...and it's below freezing tonight. If it weren't my birthday... :D

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Originally Posted by Just Jeff

But if there's air between the hammock and quilt, you're using it wrong. My quilt touches my hammock, and my hammock touches my clothes, and my clothes touch my body - with VERY little air in between - so the heat transfer is primarily conductive (especially in my DownHammock).

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You're spot-on when referring to an underquilt - your KAQ warms up much quicker, for instance, than my Marmot bag on top. That brings me to a slight difference in point, though - I was really talking about dead air spaces between the user and a TOP quilt. I guess I had my prototype quilt on my mind at the moment, which I've primarily used on top since I've had your UQ to borrow :p Incidentally, though, my top quilt "warms up" quicker than your UQ, even WITH the extra air I have to heat.

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Originally Posted by Just Jeff

Hrm...that brings up another question. What's the transfer mechanism for heat from one down cluster to another as it moves through the underquilt? Convection, b/c each cluster makes a microclime and the heat has to travel between the microclimes? A little bit of conduction obviously. And radiation? Probably even some evaporation in there...but what's the primary means? Is the convection more than the radiation?

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If I'm remembering my Thermal correctly, radiative heat transport only becomes the predominant mechanism in the high-temperature limit - MUCH higher temps than we're talking about. In this case convection is likely the primary means for heat exchange, with two reasons for my supposition. First, convection is usually predominant for "normal" temps. Second, lofted insulation is a convection barrier. It really neglects conduction altogether. This being the case, the effectiveness of lofted insulations also supports convection as the primary exchange method - if conduction were predominant, the insulations we use wouldn't work.

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Originally Posted by Just Jeff

Need to check out the new two-person hammock I just built...and it's below freezing tonight. If it weren't my birthday... :D

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I've been curious about that for a while - let us know how it works out!

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Originally Posted by blackbishop351

...high-temperature limit - MUCH higher temps than we're talking about...

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Not so quick, grasshopper...I'm pretty HOT!! :eek:

The two-person hammock worked great for the 10 min I laid in it with my 7yo. Not sure how it would be with another adult in there. And we were pretty close so it's probably not a summertime kit. Adding the spacer like Youngblood was talking about is probably a necessity for two adults, especially in summer. It'll sure be quicker to set up only one set of supports for both hammocks though.

Next addition - a hammock sock that fits over both hammocks.

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Originally Posted by Just Jeff

Not so quick, grasshopper...I'm pretty HOT!! :eek:

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I honestly have no opinion or basis for judgment on that one - better ask your wife! :p

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Originally Posted by Just Jeff

The two-person hammock worked great for the 10 min I laid in it with my 7yo. Not sure how it would be with another adult in there. And we were pretty close so it's probably not a summertime kit. Adding the spacer like Youngblood was talking about is probably a necessity for two adults, especially in summer. It'll sure be quicker to set up only one set of supports for both hammocks though.

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I've been contemplating the spreader bar solution too. Seems like it might be easier, but then again you're right about the quickness and weight savings with a single suspension. I'm sure the "normal" rated suspension is fine with the addition of your son, but do you have any thoughts on how to strengthen the supports enough for a second adult?

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Originally Posted by Just Jeff

Next addition - a hammock sock that fits over both hammocks.

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Wow...that would be HUGE :eek:

As a side note, I'm a few days away from prototyping my double-hammock tarp idea.

Thanks for the imputs.

Let me see if I am understanding this correctly and summerize your guys' thoughts on this.

From my heat transfer days I remember there being convection, conduction, and radiation forms of heat loss. From what you are guys are saying, radiation happens at too high temps (thinking hot space objects or hot ovens), convection would mean a lot of air flow which doesn't happen too much, which leaves conduction.

There is some air flow, hence the beathability of DWR. Most of it is coming from our bodies coming into contact with the hammock body, then the underquilt through that. There is some air flow, but not much.

This makes non-coated basically the same as DWR. I am going to stitch with it. Basically since I have some of it and like the feel. I like being able to swing and feel the air hit my hind parts in the hot summer months.

Now that brings another interesting question based on what BB said about his top quilt. I am not worried about my setup getting wet in my pack. In the cold months I could sub in a top quilt or peapod with with a DWR outter shell and a untreated inner shell. This would allow the user to heat up faster where the conductive heat transfer is going to take place. The DWR layer would give me the splash waterproofing layer where it would be needed. Although this would only work for synethic insulation since untreated is not down proof. Although I can almost see a synethic top quilt in my future.