Nunatak Arc Alpinist: What Customizations?

Modifications chosen:

1. Differential cut between shell & lining to reduce cold spots that might result when body presses against lining;

2. As a result of #1 above, there was a need for higher baffles (at 3" rather than 2" or 2 1/2"), which allowed more space between shell and lining for lofting;

3. which in turn maximized the benefit of the 2 ounces of over-fill that I requested;

4. Quantum shell (.85?) for light weight & breathability, with taffeta lining for strength & durability; and finally

5. had the length sized about halfway between the "long" and "medium" as described at Nunatak's website to fit my height since my height of 5' 11" is at/near the breakpoint.

Additional note: exchanged a lot of emails with Nunatak to ask questions and get educated before settling on what seemed best for my anticipated use of the quilt — which was to be either in a bivy under a tarp, or at other times inside a tent with no bivy.

At 24 ounces, very warm, comfortable, and flexible.

Great piece of gear!

JRS

Similar to above, I got: 2.5" baffle height, 2 oz overfill, differential cut, Pertex Quantum shell & Black Tafetta Lining.

I'd suggest calling/emailing Tom and discussing your sizing needs. I'd also recommend having your typical clothing kit pretty much dialed in beforehand, if you plan to integrate clothing with your sleep system.

I'm still very happy with my Arc Alpinist. Best of luck with yours!

EDIT: re-checked the specs of my quilt and corrected them above for reference

Richard & Jason,

Thanks for taking the time to give you the great suggestions based on your own experience.

When you are talking about the number of inches of the baffles, this is the height of them or the space between baffles? (It would meke more sense if it was the height of the baffles)

How much difference is there between 2.5" and 3.0" baffles? Does it significantly add additional warmth?

How much weight overall did you save by using the 0.85 Quantum fabric?

-Tony

Yes, 2.5 – 3″ refers to baffle height. The baffles on mine are spaced 5″ apart.

>How much difference is there between 2.5″ and 3.0″ baffles? Does it significantly add additional warmth?

There may not be a simple answer to that one. Given the same fill weight, the prevailing idea is that down which has enough space to loft maximally will insulate better than down which is slightly compressed. More loft = more warmth. In reality it’s not that simple. Down’s optimal density for insulative value is actually much higher (‘more overstuffed’) than it’s optimal density for loft. Richard Nisley explains this much better here.

So it’s not necessarily a bad thing when a given amount of down is slightly compressed by the baffle height. There should be a way to determine the ideal baffle volume for a given amount of down fill – ‘ideal’ for maximum warmth:weight ratio. All I can say is, good luck with that! Between 2.5″ and 3″, both with 13 oz fill, we’re probably splitting hairs here. How’s that for an evasive answer? :)

It’s probably best to focus on the loft you want for the most predictable results. I just like a higher fill density to plump up the baffles, prevent down from shifting, and to help maintain my desired loft even when things are damp. Also, I forgot to mention before that I requested 3 straps underneath, instead of 2.

Hope all this helps!

Jason,

Thanks alot for taking the time to give me your thoughts on all of this.

I am learning a lot in a short time….gotta love the people on the forums!

Last question that I can think of:

I see the value in having a third strap to create a snugger "burrito" to prevent drafts and increase warmth.

Given that I use a torso pad, I would not use the strap to go around a full size pad.

Is it a lot of fuzz to get those strap snapped and cinched snuggly around you while you are in it or do you cinch the straps to the girth that you want and then slip into the quilt for the night?

Just seems like it is like trying to ties yourself up into a bundle while you are inside of a sack….can not be easy.

-Tony

Nah, it's not too bad. I leave the straps at a set length for the most part. Unsnap the neck snap and crawl in. At most I unbuckle or re-adjust the top strap. I never thread the straps under my pad, just around myself. Knots in the straps prevent them from lengthening way too much. Realistically, the straps might stay unbuckled for all but the lowest end of the temperature range anyway.

I can empathize with the learning curve, and the deliberation process! Best of luck.

Tony,
Shoot, I don't own a Nunatak… what am I doing responding?! I just wanted to reinforce or support the idea that a shorter baffle height with overfill would optimize your warmth:weight. And, understanding this is your quilt/Nunatak research, I have to slip in a plug for a Western Summerlite w/overfill. I sleep cold, but that combo has taken me well into the twenties without anything beyond normal baselayer–21oz for a reg. Anyway, I'll shut up now.
Brad

Tony,

Regarding your question about weight differences between a Quantum shell and the other materials offered by Nunatak, there's a weight estimate provided in the chart at the following page of the Nunatak website showing information about various shell options — including total weight for a quilt with each shell option for each size:

http://www.nunatakusa.com/site07/arc_products/arc_alpinist.htm

From the chart at the above page, it appears as a general matter that a quilt using a quantum shell weighs about one ounce less than a quilt with microlight shell, which in turn weighs about two ounces less than one with Epic shell.

Also helpful is the following link at the above page that takes you to a description of characteristics of fabrics used by Nunatak, and identifying some of the trade-offs inherit in each material (weight, durability, etc.):

http://www.nunatakusa.com/site07/arc_products/arc_alpinist.htm

At the time I ordered my Arc Alpinist, I had hoped to have it in time for a fall backpacking trip that I had already planned to the Enchantments. Since there was simply no way that the quilt would be completed in time, Tom kindly sent me a demo Arc Alpinist with Epic shell for me to use on my trip. I much appreciated the Epic-shelled loaner, and not just because I had a trip planned. The loaner quilt gave me the chance to experience Epic's "loftiness" and breathability. It was excellent on both counts.

I also appreciated Epic's durability since I for sure wanted to return the loaner in fine shape. At that price, I couldn't afford more than one quilt and looked forward to having the custom version that I ordered!

Tom is of course the best source for information on the Arc Alpinist. From what I've heard and from my personal experience a few years ago, he is extremely helpful (and also extremely patient) in discussing a potential order. He has no doubt by now heard just about every question that might be imagined, which probably helps explain why his website is full of a lot of great information.

With a custom-made quilt that's so expensive, it is very reassuring to discuss options with Tom to be certain that features you "believe" you want to include in the order will in fact meet your needs and expectations.

As for straps, my quilt has the standard number (two) and I've had no particular difficulty using them if there's a need for some extra warmth. It's easy (for me, anyway) to reach under my legs, fasten the lower strap, then reach behind my back to fasten the upper strap. All of this is done while the quilt is loosely drapped over me.

I don't try to fasten the straps around my pad. Doesn't seem necessary for comfort — at least not so far.

There's an additional feature for securing the head of the quilt if needed to seal the interior for warmth. A snap connects the quilt's two corners at that end, and you can secure the corners by reaching behind your head and snapping the corners together behind your neck. There's an elastic cord sewn into the hem at that end so that the entire end can be snugged up with a cordlock once the two corners are fastened. Simple and quick.

JRS

Richard, Jason, and Brad,

Thank you again for all your great insight on this quilt.

In some ways, when the quilt is custom, there are too many choices to make!

Can any of you give a reason why a 3rd strap is important?

I am guessing that it would go behind the middle of your back/shoulder blades to keep the top from splaying open too much and causing a draft.

I typically am a back sleeper and don't move much, though I have been known to roll over at night on my belly and want to curl an edge of a blanket under my arm, which would seem to me a reason to not need a 3rd strap.

-Tony

Hey Brad, where do you get a summerlite with overfill?? At hermits hut and places like that it is always one of the bags that never has an overfill option. I thought WM just didn't offer it as an option?

Richard's post, linked above, he lists the following densities and descriptions:

2.16 kg/m^3 – density of 800 fill down in WM and like bags
24 kg/m^3 – optimum density of 800 fill down, first time
75 kg/m^3 – optimum density of 800 fill down, second time

There looks like there is a typo somewhere. Intuition tells me that optimum fill should not be more than 10x the fill UL companies use, and definitely not more than 30x the fill. It is also confusing how he states two optimum densities.

Can someone explain?

I don't think there's a typo.

Richard has linked to data which shows that you can increase the density of down dramatically more than in your average sleeping bag without causing loss of insulative power. So it's about the amount of down, not the "loft" (for a given fill power of down).

Presumably outdoor companies use an amount of down which gives as much loft as possible without having any excess material. Why? Well, a lofty bag just looks much better and warmer doesn't it! Montbell bags, for example, don't look as warm and lofty as Western Mountaineering bags (with a similar temp rating)… but according to users they are plenty warm.

Anyway, according to this theory you could jam a whole lot more down in a MB UL inner jacket without needing to make it big and puffy. I'd love someone to build a MYOG super-stuffed (thin) jacket and compare it with a standard puffy jacket.

Matt,

Thank you for pointing out the typo. In the referenced post I said the optimal density was 24 kg/m3 and then later said it was 75/kg m^3. The correct value is 24 kg/m^3. I just updated the post.

OK then, Richard can you post a graph of the relationship between density and clo/inch? Your numbers show that you could stuff 10x the amount of down in the same space to reach optimum density, but you gain only 3.03x gain in clo/inch.

All of this is in search of the optimum density, weight and warmth ratio.

Just reread Richard's posts in the other thread, and yes, I agree Matt… I'm not sure why a density of 24kg/m^3 (10+ times more dense than normal) is "optimal" if it it only increases the clo/inch by 3 times.

With clo/inch of 3 times greater, to get the same value of clo you would need only a third of the thickness of down. But since the down is 10x denser you still end up using 10/3 = 3.3 times as much weight in down.

I suspect there is something wrong with that reasoning somewhere, or one of the figures quoted, because that obviously isn't 'optimal' warmth for weight!

Matt and Ashley,

Note that the density/insulation curve is near-linear until about 7.28 kg/m^3 and then it has a very shallow slope until it reaches optimal density of 24 kg/m^3. In the predecessor threads relative to this topic, I provided three different charts to illustrate the curves for different fill powers of down. Only the near-linear portion is relevant to UL backpackers (2.5x density increase).

Thanks Richard, I think that solves the dilemma!

In that lower density region you have a linear relationship, so a 2.5 greater density of down will result in 2.5 times more clo/inch.

I think one reason the confusion arises is because 24kg/m^3 is referred to as "optimal". I would rather say the 7.3kg/m^3 density is optimal, because you can pack the down in as tightly as possible whilst still getting full warmth value for your down.

The 24kg/m^3 I would refer to as a "maximum" density… once you start to pack it in any tighter than that the clo/inch actually starts to decrease.

Ashley,

I agree that your explanation is probably easier to understand for the forum participants. What I was originally trying to convey is that every loose fill insulation type has an optimal density at which it achieves it optimal (lowest possible) thermal conductivity. The lowest thermal conductivity is the same as the highest thermal resistance. For goose down this optimal thermal conductivity is ~.025 W/m K and the density required to achieve this is ~24 kg/m^3.

Hey, Ashley-
I'm a WM dealer, and ordered it custom from them. Definitely not a stock item, or one they offer overfill on. To be honest they weren't thrilled about doing the Summerlite, but they were gracious enough (and great!) to do it for me. Since it's not a regular thing for them, I did have to wait two or three months… in my mind, worth it. I suspect that if more people made the request they'd make it a regular option, but that's just my unofficial thought. Put in a special order for one, be ready to wait, and I think you should be able to get one. Cheers-

I've been pondering some of the same issues being discussed in this thread so let me toss it out my situation. I have a golite ultra 20 that weighs 18.65 oz (w/o straps) and I have used it to 20 degrees with Montbell UL inner jacket, MLD ultralight bivy, and 3/8" CCF pad trimmed to 38" and was fine in it.

I've made the statement I can't imagine a lighter sleeping item keeping me warm using the same other items down to 20 degrees. This thread is making me think. Can a Nunatak quilt weighing 16 – 18 ounces be as warm as my Golite Ultra 20. If so what is the best way to spend ounces to make it happen.

Golite Ultra 20: down=9.5oz, wgt=19oz, baffle=2.5"

Arc Alpinist 20: down=11oz wgt=20oz, baffle=2.5"
Arc Ghost 32: down=8oz, wgt=14oz, baffle=2"
Arc Specialist 32: down=8oz, wgt=16oz, baffle=1.75"

The arc alpinist might do it if I use the lighter .8 quantum.
The Ghost might be close already, do I add 2 oz of down? Is it ok that it is narrower?
The specialist seems like a candidate, add 2 oz? but the baffle is 1.75" this is confusing.

Any thoughts on what Nunatak quilt with which options would get a bag that is better then my golite ultra 20 (weight wise) and/or warmth wise?

I wish I could leave well enough alone, always looking for something better.

Thanks,

Jamie

If the Ghost size will work with your build and sleep style you could customize by using the 2.5" baffle and a 2-3oz overfill. This would get you into the temp range of the Alpinist and save you weight. I just received mine not long ago, very nice.

Thom, Thanks for the info. I want to make sure I understand you…is your Ghost 2.5" with extra down or is yours the standard spec. If it is 2.5" and extra down is there any chance you can weigh it and let me know what you get. I agree if I can handle the tighter fit I think the 2.5" with down would be perfect.

I'm just not sure I will like the smaller size of the Ghost. I really like the size of my Ultra and I think it compares better to the Specialist size. $400ish bucks is hard to shell out to try the size.

One more question…how long did it take to get your Ghost once you ordered it?

Decisions, decisions, decisions….thanks for the help.

Jamie

Jamie, a long PM sent. I hope this helps.

Thom, I got your PM, yes it helped.

Thanks, Jamie