Spinntex as a bivy bottom?
Posted: 14 September 2007 04:06 AM   [ Ignore ]  
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I’m new to bivies, especially UL bivies.  I recently made a bug bivy, using 70 denier tent footprint fabric for the bottom, a which I think equates to 2(?)oz/sq yd, so I’m very uncertain on how something at half the weight would hold up as the bottom of a bivy.  I’m familiar with silnylon, but so far am not familiar with Spinntex.  On paper, at least, it’s a very interesting fabric, and when I think of the momentum-topped bivy that I’ll be making this fall, Spinntex seems like a better choice for the bottom than silnylon.  But, again, I don’t know about this fabric’s limitations.

Is 0.88 oz/sq yd Spinntex too delicate to be used as a bivy bottom? 

For 0.97 oz/sq yd Spinntex, same question. 

I’ll probably be using a polycro groundsheet most of the time, or at least have one in my pack in case I have to make camp on wet or muddy ground (so I can spread my gear on something dry).  Would polycro—the kind sold by Gossamer Gear—protect the bivy bottom at all against abrasion or would I have to get a groundsheet that’s actually a stronger fabric than the bivy bottom itself?  It seems like even a Spinntex groundsheet would be of zero use in protecting a Spinntex bivy bottom from abrasion because something that’s sharp enough to rub through the groundsheet would also be sharp enough to go through the bivy bottom—but maybe I’m reading too much into it and that’s not how it works in practice.

Maybe there’s another, more basic factor I should consider.  Noise.  That is, from what I have read, it seems this is a very noisy fabric.  Would it be stupid to use such a noisy fabric in an application that would put it 1-2” away from my ear? 
-I realize this is probably a matter of personal tolerance, and I’ll be finding out more about my own preference for this fabric later this week when I receive the spinnaker tarp I recently ordered from Oware.  Still, what do you think?  Too noisy to be practical in a bivy?

On a related subject, if I were to make a bivy using silnylon for the bottom, and if I didn’t use a groundsheet, and for some reason I ended up sleeping on a small puddle, is it true that water could be forced through, into the bivy, through the fabric?  If so, then since Spinntex supposedly has a thicker silicone coating, would Spinntex suffer less dramatically from this problem?

Thanks for any help,
FT

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Posted: 14 September 2007 11:54 AM   [ Ignore ]   [ # 1 ]  
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It seems like even a Spinntex groundsheet would be of zero use in protecting a Spinntex bivy bottom from abrasion because something that’s sharp enough to rub through the groundsheet would also be sharp enough to go through the bivy bottom—but maybe I’m reading too much into it and that’s not how it works in practice.

That’s just the way it works in practice.

On a related subject, if I were to make a bivy using silnylon for the bottom, and if I didn’t use a groundsheet, and for some reason I ended up sleeping on a small puddle, is it true that water could be forced through, into the bivy, through the fabric?  If so, then since Spinntex supposedly has a thicker silicone coating, would Spinntex suffer less dramatically from this problem?

Yes, it’s true: spinntex doesn’t work well in a reasonably high pressure situation like you describe.  It’s at its best as a canopy fabric.  People do use it for bivy bottoms, but it’s more for a splash-type bivy and not sleep-in-a-puddle bivy.

In terms of waterproofness, the hydrostatic head pressure is between 1 and 2 psi.  This is a little bit less than 1sts quality sil nylon.  Its much less, though, than a fabric used in commercial bivy bottoms which usually have very thick coatings of polyurethane.  Typical fabrics waterproof enough for use as a real bivy bottom weigh upwards of 3 oz per square yard.

AYCE

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Posted: 16 December 2007 05:16 PM   [ Ignore ]   [ # 2 ]  
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Finley_Thomas - 14 September 2007 04:06 AM

Maybe there’s another, more basic factor I should consider.  Noise.  That is, from what I have read, it seems this is a very noisy fabric.  Would it be stupid to use such a noisy fabric in an application that would put it 1-2” away from my ear? 

FT

Ayce, so is this fabric noisy ? I also want to make a bivy.

Thanks

Mike

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Posted: 16 December 2007 05:37 PM   [ Ignore ]   [ # 3 ]  
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It is more noisy than other bivy bottom choices such as 1.1 sil or PU-coated fabrics, yes.  It is less noisy than some things commonly used as a ground cloth, such as mylar space blankets.  If crinkley-type noise is more important than weight you would be happier with something else, but I personally wouldn’t consider it to be a show stopper.

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Posted: 01 January 2008 01:20 AM   [ Ignore ]   [ # 4 ]  
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I made the spinnaker/momentum bivy recently and here’s my thoughts on it…  It definitely is a crinkly/noisy fabric, kind of like a plastic grocery bag.  However, as it is “broken in”, it gets a little quieter.  Also, the crinklyness gets muffled by my quilt or sleeping bag, but the part underneath my head is pretty noisy—not too noisy that I can’t sleep, but it’s an inch or less away from my ear: you do the math.  If I make another bivy, or if I modify this bivy, I’ll use silnylon under my head. 

The spinnaker definitely contributed to an overall low weight.  The finished weight is 5.5 ounces.  I used an ‘over the chest’ style #3 zipper, 2-layer Gore-tex with an Activent face fabric (~3osy) for the footbox, and rather snug dimensions (I ended up having to modify the top because the bivy was too short for me at first). 

I don’t believe durability is going to be an issue.  The spinnaker is a little easier to cut with scissors than silnylon, but doesn’t seem like it would wear down under normal use.

Overall, I’m definitely pleased with the fabrics I used for this bivy, but the Gore-tex footbox and the spinnaker bottom are both overkill.  A momentum top and silnylon bottom would have been just fine, and probably would have weighed about 6 ounces or less, given the same dimensions.

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