Montbell Seamless Down Sleeping Bags

[Geoff Caplan]

Roger

Who wants to sleep in a straight jacket anyhow?

One thing I’ve learned from this site is that people’s sleep preferences vary widely.

After a few years of experimentation I’ve found that I actually prefer sleeping in a bag than a quilt. And I don’t even need all the width in my current bag – my next iteration will be narrower to save weight.

I guess that’s why there are so many options on the market – we all prefer different things.

[Roger Caffin]

Vive la difference!

[Ross Bleakney]

Do you need a ‘stretch’ bag anyhow? Who wants to sleep in a straight jacket anyhow? I prefer a loose quilt.

The whole idea of a “stretch” bag is that it has the comfort of a quilt, with the warmth of a normal sleeping bag. It is not a straight jacket.

Most walkers sleep happily without one.

Most? You mean most backpackers are using quilts these days? Last I checked sleeping bags greatly outnumbered quilt use.

 

 

[Roger Caffin]

Hi Ross

No, that was not what I wrote. I wrote
Most walkers sleep happily without one.
where ‘one’ fairly clearly refers to a stretch bag.
My reference to my quilt was an aside.

‘Straight jackets’ might have been a slight (but only slight) exaggeration. One of the reasons many walkers use quilts is that you can’t stretch out inside an SB, but you can under a quilt. I tend to have my legs at strange angles in bed at home, and I like to be able to do that when camping.

But, to each his own.

Cheers

[Sam Farrington]

“Anyone have an opinion on that patent, particularly with regards to potential for durability?”

Thanks for digging out the patent.  But I plowed through most of it and found no guide to durability.  As was pointed out, the only hint is in the washing instructions.

So it appears that MB has come up with a down batt, held together by an unknown adhesive.  The patent uses the terms “glue” and “binder,” but did not find a reference to the term “yarn”  used in the marketing.   But threads could well be involved in holding the batts together and maintaining their shape.

Also, there was some suggestion that the stretch of the  outer material is “multi-directional,”  suggesting that it is not a woven cloth.  If they have also come up with a superlght non-woven fabric, with controlled elasticity in all directions, that could be as innovative as the down batt.  And if the material is “airtight,”  does that mean it is water tight as well?  And even if it is airtight, it might still be water vapor permeable.

Was just looking at an old MB insulated jacket today, and the label in the inseam says “made in China.”  It may be quite a task for MB to protect its patents.  Assuming that all works itself out, I envy our posterity with their more efficient warmies and shelters that weigh next to nothing.

Am with those who revel in the elasticity of the MB spiral stretch bags.  When Will Rietveld reviewed the first ones, bought one at once.  Warm at 30F without wearing puffies or fleece, and weighing 20 oz in the stuffsack.  It’s still like new.  As a restless sleeper, agree that one must try one to see how comfortable they are.

[Ryan Perkins]

Hmm I wish Montbell would publish the weight of the down fill.. but maybe because it lofts differently they don’t think it’s comparable. Wonder if their temperature ratings are a little conservative, since the ISO test doesn’t capture things like air flow and vapor, which these bags handle differently.

Really wish they made a quilt version.. I might just get one and cut off the hood and zipper, see how light it ends up :)

[Stumphges]

Ryan, I think turning it into a quilt would defeat the purpose. Montbell’s Superstretch bags are better than quilts, in my experience: they allow greater freedom of motion while sleeping than quilts do because they stretch to accomodate motion while disallowing drafts. If you turned it into a quilt you’d just have a stretching quilt but movement would be constrained to avoid letting drafts in. Well, maybe if it was very well-secured to the pad it would still be nice to have stretch. Hmm, don’t know. I’m glad I didn’t start this post with a dogmatical statement.

[Eric Blumensaadt]

Hmmmm… I’ll be interested to see how it works over time with repeated stuffings i.e “durability” as others here have questioned.

[Ryan Perkins]

Yeah good point about the benefit of sealing out drafts. Maybe I’ll cut off the zipper and sew it shut (someone makes quilts like this, can’t recall right now.. cumulus?). If it’s really that stretchy, this construction which sounds constricting to me would work fine. Maybe I can even make a shock cord cinch for the foot so it can be opened if it gets too hot.

Sounds like an expensive experiment, but I can be the guinea pig tester for durability.. think I might go for this.. now should I get the Gore Tex Infinium version? 1.7oz/$140 heavier for their 30º bag…

[Stumphges]

Ryan, I think Montbell shortened the zippers on these to half zippers, right? Maybe that’s short enough? (Although one of the truly awesome things about Montbell Superstretch bags is two of them zipped together for couples!)

Cutting the hood off, if the model has a draft collar, is a fine idea. I’ve come to favor well-sealed neck openings and hoods. With a Superstretch bag it would work great – being able to spin inside a stretchy bag might turn out to be the acme of backcountry sleeping comfort.

[Ryan Perkins]

Interesting, it looks like the goretex-shelled version has a 30″ zipper and the non-GT version is about twice as long. The goretex one is a waterproof zipper, not sure about the non-gt but maybe they shortened it to offset that weight.

Yeah I’m even thinking you could get away with a “slimmer fit” bag with less material if it’s stretchy.. so lower weight without sacrificing loft/comfort, and not needing a zipper. Would love other design suggestions here while I’m tearing up an expensive bag :)

[Stumphges]

Sam, I fear I’ve led you astray with that patent. I think the one I linked to is the wrong one. I recall asking MB by email what the patent ap # is for Spider Baffles and never getting a reply. Just tried searching again and failed.

[Dan]

Yeah I’m even thinking you could get away with a “slimmer fit” bag with less material if it’s stretchy..

Based on my experience with the previous generation, the bag is a little roomier than necessary for me at 5’9″ 150lbs.

[Ryan Perkins]

Cool, just ordered the non-gore tex #3 (30º limit bag).. I’ll see if I can slim it up when I sew up the zipper. Anyone want to get a wager going on how much weight I’ll remove by trimming the zipper and hood? It’s starting at 17.4oz.

[J-L]

I think you’ll drop the weight to 14oz, maybe 13oz depending on how much girth you remove. It will be interesting to see what the down looks like inside (post pictures!) and I’m curious how you’ll handle sewing the down back to the shell. It might be easiest to stitch through the shell and liner first, then cut away the excess, and do a lightweight binding over the raw edge. Just guessing.

[Stumphges]

Ryan, you might want to read the description of spider baffles again b4 cutting. U might be opening a spiders nest. (But I hope u do it anyway and post pics;)

[Ryan Perkins]

Yeah I also thought just stitching through the whole thing before cutting off the zipper might be the easiest way to do it, but I’ll rip a seam at the zipper first to see what the inside looks like and how that spider down is anchored if at all. Maybe I can identify a cleaner way to do it. Depending on how the loft looks, and how much weight I end up trimming I might go back and take out some down.. I’d love a sub-12oz 30º limit bag, wondering if it might be possible here.

Plus I’ll end up with a whole hood of extra material, maybe I’ll make it into something I can snap onto the bag if I don’t feel like sleeping in a hooded down jacket for whatever reason.

Might go crazy and use some of this bemis bond or iron-on seam tape that’s been working well for me on other stretchy things, we’ll see!

[Roger Caffin]

OK, this is a biased opinion, and doubtless many will disagree. However, here goes …

Cutting the hood off is about the silliest thing you could possibly do. The weight involved is trivial, but the warmth the hood will give your whole body is worth half a kilo of extra down. Keeping your head warm in cold weather is the single most important thing you can do. It even outweighs having a better pad under you.

My 2c
Cheers

[Ryan Perkins]

Well, I’m a very silly person, so that would be right up my alley!

So you’re saying that for all quilts, an integrated hood will offer a better warmth:weight ratio than a hoodless quilt plus a down jacket or a down hood (garment style) or a warm hat? I could see that being true, since your head shares the same air pocket as your body in a sleeping bag, but not in those other solutions, and it only requires one seal closure rather than two.

Regardless, my goal isn’t necessarily to maximize warmth here, I just want something that weighs as much or less as a 40ºlimit down quilt that’s a bit warmer.. maybe approaching a 30º limit quilt (not bag). I definitely wouldn’t be taking this thing anywhere near freezing, at least not with a second quilt.

[Roger Caffin]

since your head shares the same air pocket as your body in a sleeping bag,

Yep

Cheers

[Geoff Caplan]

Let’s go with the drift…

I’m having a dither about a built-in hood for my current 20F bag project.

In theory I’m agreeing that you gain warmth by sharing the same air pocket.

On the other hand, I’m a great believer in a good seal around the neck – I’ve found by experiment that this adds a lot of warmth for very little weight. So there’s hopefully not much heat leaking out from the main body and into the hood.

Clearly if the neck’s not sealed as in Roger’s pic the hood will be trapping more body heat so it depends on usage.

More significantly I’ve just checked the hood on my old 2C/36F Rab bag (300g/10.5 oz high quality down), and realised that the down is horribly clumped and lacking in loft. I can’t tease it out, and I’m pretty much only getting insulation from the fabric. It seems that the down has been flattened by the oils from my scalp. So in practice I’m not getting efficient insulation. I’d estimate 100 nights since it was last laundered – looks like a wash is overdue…

Tim Marshall at EE recommends Apex for hoods – he feels it stands up better to oils and moisture. Looking at my bag, I suspect he’s right.

So, potential advantages of a separate hood:

1)  Apex can be laundered much more easily, especially on the trail.

2) You can match your headgear to the conditions.

3) You can wear your headgear around camp and huts.

4) With open back systems that don’t turn with the sleeper, the hood will turn with you and not cover your face.

5) You can replace your hood if it loses loft. I suspect the down in a built-in hood would be the first thing to go on a bag, so a separate hood may extend the bag’s life.

6) A purpose-built hood may have a more efficient cut than a typical mummy hood?

So thinking it through it seems that the inclusion of a built-in hood isn’t quite the open-and-shut argument I’ve always assumed. At least for longer trips a separate hood may work better in practice.

Really just thinking aloud here, but hopefully someone will find this useful…

[Ryan Perkins]

Yeah I’m not really convinced either way – it might come down to personal preference or how you move when you sleep. Here’s some facts/assumptions maybe we can agree on?

1. Sharing a pocket of air between your body and head is good so that your body heat can help keep your head warm.
2. Preventing the pocket of air inside the bag/quilt from escaping with some kind of seal is also good.
3. A quilt can’t enable sharing of the air pocket because it needs to seal off around your neck to prevent the air from escaping.
4. A bag needs to seal off around your mouth, nose, or face to prevent air from escaping. For some people, this seal might be harder to maintain throughout the night if you’re moving your face around, or it might be too uncomfortable for others.
5. A jacket or garment hood could have a higher insulation:weight ratio than a bag’s hood since the fitted pattern could use less insulation area for the same loft and less shell material (though I’m sure some of them are less efficient), AND can be used outside of the bag, eliminating the need for a second insulation layer on some trips.

So to me, seems like it comes down to whether you find it possible and comfortable to maintain a good face seal with a bag’s hood, or whether that air will leak out enough to make a jacket/garment hood warmer despite not sharing the air pocket with the body. I think in the case where you can comfortably maintain that face seal to some extent all night AND you don’t need a second insulating layer, the hood on the bag is probably better even if it has a somewhat lower insulation:weight ratio.

So all that makes me think we should come up with some designs that make the best of both worlds, like a removable hood that seals to the bag on one end, and your face/mouth/nose on the other so that the warm air pocket can be shared. Then the removable hood can be worn around camp so you don’t need a second insulation layer (so maybe it needs to extend down over the torso a little. Of course the challenge is achieving these seals without adding so much weight or tamping down loft that it offsets the benefit. Makes me think maybe a mummy bag that goes up to your waist, then zips or snaps to an upper portion that’s basically a hooded jacket with no sleeves or maybe some sealable arm holes so that you can wear it around camp would be a cool novel solution. I’ll think about if I want to try this when I butcher this montbell seamless bag.. would love some more ideas/suggestions!

[J-L]

I agree with all your points, Geoff. You summed them up well.

In my MYOG down quilt, I’ll get cold at about 35F with it just draped over me. Add a Goose Feet Gear down hood and cinch my fully baffled neck closure up, and I’m good to at least 20F (haven’t gone lower). The warmth gain from the hood/neck seal is incredible. I personally think hoodless, zippered sleeping bags are going to be the best middle ground for most people and we’ll see more of these designs in the coming years.

I found that Western Mountaineering publishes their EN ratings under the FAQ section of their site. So I plotted the EN Comfort ratings for the SummerLite and UltraLite and the ISO Comfort ratings for the Montbell Seamless bags. There’s actually a fairly linear trend between comfort rating and weight. The only Montbell bag that sticks out is the Seamless #3 – it’s 2F warmer than the Summerlite and 1.6oz lighter (not a big difference at all). One caveat here is I don’t know if ISO and EN methods give different ratings. Plotting Limit Rating gives the same relative trend, just all the points are shifted downwards.

Given that the Western Mountaineering bags are using heavier shell fabrics and heavier zippers, they must be significantly narrower to achieve similar warmth per weight as Montbell.

[Roger Caffin]

I would like to address some of the points being made here.

Neck seal
Yes, indeed, this can be important – under certain conditions. The photo I showed is of a summer weight quilt being used down to 0 C. You don’t get much of a neck seal with a quilt though. Sue has created a neck seal by pulling the quilt around her neck so that only her face ‘sticks out’.

Hood insulation and skin oils
Yes indeed, the effect of skin oils on the down is important. Basically, you don’t want any transfer of skin oils.
What is not visible in the photo is the fact that Sue is wearing a ski cap of light fleece so her skin is not in hard contact with the quilt. She also wears this cap when it is cold while eating dinner or breakfast of course. Multi-purpose.

It was warmer this night, so she is happy with the quilt just around her neck. It still makes a seal though. Also, if you look closely, you can see that her face is resting on her pillow rather than on the quilt. The pillow fabric and the ski cap get washed after every trip.
Do a small check for yourself: do you sleep at home on an insulating pillow with the quilt over your head, or do you sleep with your head on the quilt?

With open back systems that don’t turn with the sleeper, the hood will turn with you and not cover your face.
No, the opposite happens.
What happens at home when you turn over? Does the quilt move across the bed with you, or do you turn under the quilt? The same applies here. The hood sits on top of you, and you turn under it.

A quilt can’t enable sharing of the air pocket because it needs to seal off around your neck to prevent the air from escaping.
Not really. It does not need to seal off around your neck. It only needs to seal off at the front. You can have free flow if you wish at the back of your head.

Removable Hood
The problem with a removable down hood is that it becomes very hard to stop skin oils from getting into the down, because you almost invariably end up with your head resting on the down. On the other hand, Sue’s ski cap is effectively a ‘removable hood’.

YMMV. This works for us.
Cheers

[Geoff Caplan]

John

It’s difficult to know what’s going on with the Seamless bags – on the EU website at least, they don’t give the fill weight, which is naughty as you don’t really know what you are buying.

The unstretched measure is actually a bit narrower than the WW equivalent for the couple I looked at.

And while I know the Huggers have a lot of fans, I do wonder what happens when you press against the inside of the bag and stretch it. With a conventional differential cut the loft should be preserved. With the Hugger, it’s hard to see how the down isn’t getting crushed as the inner presses against the shell. Or am I missing something?

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