Bivy/Sleeping Bag/Jacket…what type of shell?

[Bri W]

Hey there! I’m not sure if this is the right place to post, but I need some advice on a multi-purpose build that Nunatak is doing for me.

Just a bit of background…I am engrossed in ultrarunning and fastpacking. I have found that with fastpacking (mostly running, some speed hiking), superultralight gear is ideal, but fewer items/more compact gear seems to be even more important, as my running vests/packs do not have much space (usually less than 20L). So because I have had such good experiences with my Nunatak 0° Raku and 30° Arc half-quit and Skaha hoodie (all of which are in down), I asked if they could do a custom project that will not only act as my sleeping bag, but will also act as a waterproof bivy and a piece of insulation apparel for around camp or (more rarely) on the move. Essentially, its upper half is the Skaha hoodie with short-sleeve arms and the lower half is a tapered, narrow Raku (cinchable open footbox that can hike up to my waist). The core is equivalent to 42° APEX and the “legs,” hood, and short-sleeve arms are 50° APEX. While down would of course be more lightweight and compressible, I chose the APEX because it handles moisture a bit more efficiently and it would allow me to tape the seams more easily and make this build into a bivy (too many seams with down baffles). Also, I did not want my warmth to be compromised by unexpected rain or my own sweat. The liner will be 0.66 MEMBRANE. The outer will be an ultralight WP/B fabric.

Here is where I’ll need advice…

I need to decide between a shell with 0.74 oz. ROBIC or 1.4 oz. DryDome (RSBTR’s relatively new 10D WP/B fabric with a hydrostatic head of >9000mm). I initially thought about the 0.74 oz. fabric because of its weight and lower bulk, but its hydrostatic head is only “>1000mm” While I do not ever plan to fastpack in bad weather, unexpected bad weather is always a possibility. Generally, my trips are 1-2 nights in Spring through Fall either in the SoCal desert (dry, low chance of rain), in the Sierras (depends on mountain weather), or in Southern Oregon (moderate-low humidity, low chance of rain). Has anyone had experience with the ROBIC fabric and its ability to handle moisture? I would use this bivy/sleeping bag/jacket with a ground sheeet, but any advice on its strength? I have experience with the DryDome, I just need advice on this other fabric. What would you choose in this type of situation and why?

 

And for extra hypothetical info if it were to rain…

I’ll be wearing my VBL clothes to sleep for added warmth. The VBL clothes also serve as my emergency rain protection. To protect my face if it were to rain, I would either put my rain jacket over my face or build a “micro” angel-wing cuben tarp for absolute emergencies (and gear protection). Still contemplating this last idea…

Obviously the cinchable open footbox is another potential entry-point for moisture if it were to rain, so I would either place the ground sheet over the open section or my rain jacket if I had the hypothetical micro tarp over my head.

 

[Michael Gillenwater]

unfortunately, i don’t have any insights on your fabric selection question.  But, I applaud your experimentation. The system I use for fastpacking is just a standard EE quilt, supplemented with a ex light puffy and a Zpacks pocket tarp.

If you can sleep comfortable in a VBL in non-winter temps, then I’ll be fascinated to hear how your system works.

[Bruce Tolley]

So your question seems to be how well will the 9000 hydrostatic head material perform in the conditions when no rain is forecast?  But then the real question is how well it will perform in the corner case?  The 1/2 inch of SoCal rain during a thunderstorm?

[Bruce Tolley]

So your question seems to be how well will the 9000 hydrostatic head material perform in the conditions when no rain is forecast?  But then the real question is how well it will perform in the corner case?  The 1/2 inch of precipitation during a thunderstorm?

[Bri W]

I guess I’m just looking for real-world experience and how it compares to RSBTR’s lab results. Especially since the Robic material says “>1,000.” I have never worked with a material at this rating in light precipitation or short thunder storms.

[Paul S.]

1000 would work for rain but I’d worry about pressure against the ground. Water would pool between your ground sheet and your bag.

[Bob .]

Perhaps also consider Argon 67 for the liner.  It is .67 oz per sq yd and has a gridstop.  I used the .66 membrane in my first quilt and Argon 67 in my second.  I like the Argon 67.  There is also an Argon 90.

[Bri W]

@mwgillenwater I’ve tried the pocket tarp but it was too long. I’m only 5’5”. I wish they’d allow me to custom order one that was a foot shorter. As far as the VBL system goes, I’ve used it all year round with great success. I’m a very cold sleeper, and I toss and turn a lot, so the VBL supplement is always lovely (except in humid environments). My coldness is also the reason I’m looking at a sleeping bag instead of a quilt. I’ll post some updates on the project after a few trips this Spring and Summer.

@pschontz I didn’t think about that. Hopefully I’m not in a situation where it’s raining that much, and site selection will hopefully reduce that risk, but that’ll be good to keep in mind. Thanks!

@bcbob I used Argon for a bivy top in the past, and while I liked the breathability and strength of it, I really like the silky feeling and breathability of the 0.66 membrane. Plus, I’m ordering it in hot pink. :)

[Nicolas]

@bwrightback have you or anyone else had read world experience with the two fabrics you asked about (https://ripstopbytheroll.com/products/0-74-oz-mtn-7d-ripstop-nylon and https://ripstopbytheroll.com/products/1-4-oz-10d-waterproof-breathable?variant=26260522305)? I am curious how prone those are to condensation (compared to eVent).

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