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Marmot Hydrogen Sleeping Bag Review

The Hydrogen is a well designed, high loft, roomy, warm, mummy-style down 30F-rated sleeping bag, but its shell fabric is heavy and wets out too easily.


Overall Rating: Recommended

Many people like to compare a sleeping bag to its Western Mountaineering equivalent – which is considered the gold standard. The Marmot Hydrogen has 850+ fill power down and has 1 ounce more down in the bag, but it has a wide cut while the WM SummerLite has a slender cut, so the loft comes out the same. The Hydrogen’s zipper guard/draft tube design is almost as good as that in Western Mountaineering bags (which have a stiffening tape on both sides of the zipper), and the hood design is equally as good. However, the Hydrogen uses comparatively “heavy” shell and lining fabrics that wet out too easily, allowing the bag to absorb moisture. For a larger person and for extra room to wear clothing inside the bag, the Hydrogen has the edge over the slender SummerLite, and it’s also more durable.

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by Will Rietveld |


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The Marmot Hydrogen is a 30F-rated mummy-style bag featuring 850+ fill power down, a full-length zipper, lots of loft, and a well-designed, easy to operate hood.

Ultralight backpackers have different preferences for a sleeping system, depending on their location and style of travel. I normally backpack in the Rocky Mountains spring through fall, and spring and fall in southern Utah, where nighttime temperatures frequently drop below freezing. I want the lightest sleeping bag that will do the job, but still want a sleeping system that will handle the occasional unexpectedly cold night. My preference is a 30F-rated mummy-style down sleeping bag with enough girth so I can wear extra clothing inside to extend its warmth when needed. Backpacking Light will publish a State of the Market article on this subject in spring 2010; this review is a separate evaluation of the popular Marmot Hydrogen bag.

The Marmot Hydrogen is the quintessential ultralight down sleeping bag, dating back almost to the beginning of ultralight backpacking’s popularity. The original Hydrogen had a half-length zipper and 10 ounces of 800 fill power down - which was state of the art at the time - and weighed 24 ounces. Review ratings of the Hydrogen have fallen in right behind Western Mountaineering bags, which is very good. The current (2009) Marmot Hydrogen is better than ever, or bloated a bit, depending on your point of view.


The latest Marmot Hydrogen, at 25 ounces, has gained 1 ounce of weight, making it 3 to 6 ounces heavier than many competing bags with a 30-32F temperature rating. However, before you scratch the Hydrogen off your list in favor of a lighter bag, it’s important to look at the specifications. The Hydrogen now has 850+ fill power down - the best to be found, save for super premium 900 fill power down - and a size Regular contains 11 ounces of down compared to 10 ounces in the original Hydrogen and many other 30F-rated bags (including the Western Mountaineering SummerLite). I measured double layer loft at 4 inches (2 inches of single layer loft), which is very good. (Down fill power is the expanded volume, in square inches, of one ounce of down.)

Another notable difference is the Hydrogen now has a full-length zipper, and I mean full-length: it ends a mere 7.5 inches from the foot of the bag. This is one feature where your feelings about it are dictated by your point of view. On the one hand, many hikers insist on a full-length zipper so they can open it up like a quilt on warm nights, use it to cover two people, or more easily couple two bags together. Then there are the gram pinchers and mountain hikers who can get by just fine with a short zipper or no zipper at all, preferring to save the weight. One thing appears to be clear - more manufacturers are going to a full length zipper, based on “user input,” and they are probably right: The number of folks who prefer the full-length zipper is bigger than the number of those who do not like it.

Other design features on the Hydrogen have essentially remained the same, with material upgrades as better components become available. There is a 1.5-inch stiffening tape between the zipper and an oversized down-filled draft tube to avoid snagging (more on that later) and to fully insulate the zipper. The hood has six down chambers and covers the head the same as Marmot’s 8000 Meter Down Parka. It closes with a simple braided drawcord and cordlock that work smoothly. The zipper is an YKK #5 CN auto-locking type with two pulls, so the foot of the bag can be opened for ventilation when needed. There is no Velcro tab at the top of the zipper, so the Hydrogen is a Velcro-free bag.

marmot_hydrogen_bag_review - 2
The zipper guard on the Marmot Hydrogen consists of a 1.5-inch stiffening tape between the zipper and draft tube on the top side and a grosgrain tape on the bottom side.

So far I have only accounted for 3-4 ounces of extra weight compared to lighter bags. The remainder appears to be due to Marmot’s use of 1.2-ounce/square yard shell fabric and 1-ounce/square yard lining, which is significantly heavier than MontBell’s 0.86-ounce/square yard Ballistic Airlight used in the Spiral Down Hugger, Western Mountaineering’s 0.9-ounce/square yard Extremelite fabric, and Nunatak’s new 0.8-ounce/square yard Pertex Quantum. The heavier fabric adds 1-2 ounces to the weight, but it also adds an increment of durability and warmth.


marmot_hydrogen_bag_review - 3
I slept in the Marmot Hydrogen on a variety of trips during the summer and fall, with nighttime temperatures ranging from 25-50F. On this particular trip I camped at an alpine lake at 12,000 feet, where the overnight temperature was 36F and breezy.

Overall, I found the Hydrogen to be a little warmer than 30-32F bags I have recently tested (The North Face Beeline, Mountain Hardwear Phantom 32, and MontBell Spiral Down Hugger #3). Wearing only microfleece long johns and wool socks inside the bag, I had no trouble staying warm down to the bag’s 30F temperature rating. Wearing my camp clothing (insulated jacket and pants, windstopper fleece cap) inside the bag, I was warm as toast down to 25F and could have managed a few degrees lower without getting chilly.

The numbers in the comparison table below account for the Hydrogen’s additional warmth: the Hydrogen has 850+ fill power down and 1 ounce more down than the other bags listed. The bag has continuous baffles, so it’s possible to shift more of the down to the topside, if desired. According to our table of estimated temperature ratings based on measured loft (read our Backpacking Light Position Statement on Sleeping Bag Temperature Ratings), 1.8 inches of single layer loft translates to about a 30F rating. The Hydrogen exceeds that target, which gives it an extra increment of warmth. Please read the referenced article and note that sleeping bag warmth depends on a number of factors.

marmot_hydrogen_bag_review - 4
The Hydrogen’s initial loft and warmth were so noticeable that I decided to perform a comparison test to get some numbers. I improvised a heat retention test to compare the Hydrogen with the Montbell Spiral Down Hugger #3, which is closer to the “standard” loft (1.8 inches single layer) for a 30F sleeping bag. I placed a covered pan containing one gallon of 125F water in the chest area of each bag (left) and recorded the rate of temperate loss overnight with a Kestrel 4000 Pocket Weather Meter in each bag. The plotted data (right) show that the Hydrogen cooled down less during the night, indicating that it provides more insulation. The actual difference in the morning was 6.6F.

marmot_hydrogen_bag_review - 5
I noted in the heat retention test that the fabric on the Hydrogen was wet (left) where heat from the pan of water inside melted frost on the outside. On another cold night I found that the bag’s fabric wetted out around the head area (right). I weighed the bag and found it absorbed 3.6 ounces of moisture that night. A water puddle test on the bag confirmed that the bag’s fabric does in fact wet out over time.

I really like the Hydrogen’s zipper guard, draft tube, and hood. They come together to create a tightly sealed bag nearly devoid of drafts. With a little practice, the zipper slides smoothly with minimal snagging, and is well insulated by the oversized draft tube. It helps to straighten both sides of the zipper before closing it.

marmot_hydrogen_bag_review - 6
The Hydrogen’s Nautilus hood is one of the best to be found; it surrounds the head and draws down to a small breathing hole around the mouth. I couldn’t find a purpose for the small down tube on the right.

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A lightweight (0.7 ounce) stuff sack is provided with the Hydrogen that is properly sized to stuff the bag without over compressing it. Kudos to Marmot!


The following table compares the Marmot Hydrogen with some popular 30-32F rated ultralight mummy style down sleeping bags. All of the bags have baffled construction, and all data are manufacturer specifications for a size Regular bag.

Manufacturer Model Temperature Rating (°F) Measured Single Layer Loft (in) Fill Weight (oz) Fill Power Total Weight (oz) Cost US$
MontBell* UL Spiral Down Hugger #3 30 1.9 10 800 19 229
Mountain Hardwear Phantom 32 32 2.0 10 800 22 290
Western Mountaineering SummerLite 32 2.0 10 850+ 19 315
Marmot Hydrogen 30 2.0 11 850+ 25 319
The North Face Beeline 30 2.4 10 850+ 22 279
*Note: A size Regular MontBell bag fits to 5 feet 10 inches, while the other bags fit a 6-foot-tall person.

From the data, the Marmot Hydrogen matches the Western Mountaineering SummerLite in down quality, fill weight, and loft. It weighs 6 ounces more and the cost is about the same. The MontBell Spiral Down Hugger #3 is one of the lightest bags, and it’s a great value, but it’s not as warm as the Hydrogen.


While the Marmot Hydrogen has equivalent down quality and loft compared to the Western Mountaineering SummerLite, it is also a roomier bag (shoulder/hip/foot 62/58/40 inches versus 59/51/38 inches for the slender SummerLite), which means there is more area inside the bag to warm up. It’s entirely possible that the two bags may be equivalent in warmth, but I have not tested the WM SummerLite, so I have no personal experience to compare it with the Marmot Hydrogen. Don Wilson reviewed the WM SummerLite, but he makes no mention of the bag’s warmth, noting that a sleeping bag’s warmth depends on a large number of variables. I agree, but in my sleeping bag reviews I will at least try to compare sleeping bag materials and design characteristics that contribute to warmth. In mummy style sleeping bags, more so than in down garments, the amount and quality of down is a useful factor in estimating a bag’s warmth. However, that assessment needs to be adjusted for factors such as the bag’s cut (slender versus roomy) and other factors. It’s easy to get sidetracked and compare sleeping bags entirely by their weight, purchase the lightest one, and end up disappointed. It’s also important to look at the amount of down in the bag, design features, and sizing. There are substantial differences among bags with the same temperature rating; not all 30F-rated sleeping bags are created equal.

Overall, the current Hydrogen is better insulated and warmer than the original and easily meets its claimed temperature rating. It also has a nearly snag-proof zipper and an excellent hood. However, it uses heavier shell and liner fabrics, and the shell fabric wets out, allowing the bag to absorb moisture more readily than other bags. It also has a longer zipper, which adds weight. Its wider cut provides extra room for a larger hiker, but it’s a little too roomy for a slender person.

Specifications and Features

Manufacturer Marmot (
Year/Model 2009 Hydrogen
Style Hooded mummy with full length zipper
What’s Included Sleeping bag, stuff sack, cotton storage bag
Fill 850+ fill power down, 11 oz (312 g) size Regular, 13 oz (369 g) size Long
Construction 5.5 in (14 cm) stretch tricot continuous baffles, trapezoidal footbox, six chamber hood
Measured Loft 4 in (10 cm) average double layer loft (manufacturer specification not available)
Manufacturer Claimed Temperature Rating 30F (-1C)
Stuffed Size 10.5 x 7 in (27 x 18 cm)
(size regular tested)
Measured weight: 1 lb 9.2 oz (714 g)
Manufacturer specification: 1 lb 8.8 oz (703 g)
Regular: 62/58/40 in (158/147/102 cm)
Long: 64/60/42 in (163/152/107 cm)
Sizes Regular fits to 6 ft (1.83 m)
Long fits to 6 ft 6 in (1.98 m)
Fabrics Shell is 1.2 oz/yd2 (41 g/m2) nylon ripstop with DWR
Lining is 1.0 oz/yd2 (34 g/m2) polyester taffeta with DWR
Features Full-length zipper with two pulls, trapezoidal footbox provides more foot room, oversized down-filled draft tube, stiffened zipper guard, six-panel baffled hood with muff to avoid zipper contact with face, ground level seams
MSRP Regular US$319
Long US$339

Disclosure: The manufacturer provided this product to the author and/or Backpacking Light at no charge, and it is owned by the author/BPL. The author/Backpacking Light has no obligation to review this product to the manufacturer under the terms of this agreement.


"Marmot Hydrogen Sleeping Bag Review," by Will Rietveld. (ISSN 1537-0364)., 2010-01-05 00:05:00-07.


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Marmot Hydrogen Sleeping Bag Review
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Addie Bedford
(addiebedford) - MLife

Locale: Montana
Marmot Hydrogen Sleeping Bag Review on 01/05/2010 15:00:11 MST Print View

Companion forum thread to:

Marmot Hydrogen Sleeping Bag Review

David Stenberg
(dstenberg1) - F

Locale: South
Wm megalite on 01/05/2010 15:37:40 MST Print View

Thanks for the review Will. It seems that the hydrogen and the wm megalite are more similar and a closer comparison than the summerlite. The manuf.specs for the megalite are 24 ounces total weight with 12 ounces of down and a girth of 64"/55"/39". They both have a full zipper too. I am a megalite user and like the width in the shoulders, though I have been tempted to squeeze into a summerlite for the weight savings.

Ed Barkowski
(edbarkowski) - F
owned and loved on 01/05/2010 17:40:58 MST Print View

Great, thorough review, Will. As usual.

I have the Hydrogen Long and really like it. Of the 7 bags I've used/owned in this temp range, Marmot's ranks among the finest. Well designed and superbly-executed construction. But, boy does that white zipper stand out!

Emmett Lyman
(ejl10) - F - M

Locale: Mid Atlantic
Nice review on 01/05/2010 19:36:52 MST Print View

Thanks, Will. I'm using a Long Hydrogen right now, and though I've been tempted to downgrade to something lighter, I can't really find a compelling replacement. This review confirms what I've seen - there are lighter options, but the Hydrogen remains a solid choice.

Matt Lutz
(citystuckhiker) - F

Locale: Midwest
Re: Nice review on 01/05/2010 19:56:11 MST Print View

Emmett, I've had a similar thoughts and always end up keeping my Hydrogen. I have a 2007 model with the 1/2 zip, and love it. I wish it had a narrower cut (and I knew about narrow cuts when I bought the bag), but alas.

Ryan Linn

Locale: Maine!
Re: Marmot Hydrogen Sleeping Bag Review on 01/05/2010 20:02:51 MST Print View

Will, I love the comparison test. Come to think of it, these kinds of technical tests are pretty much my favorite thing about BPL articles. Anyone can do a subjective spend-a-night-in-the-sleeping-bag test, but it takes a much more creative mad scientist to think of sticking a pan of hot water in your sleeping bag. Cheers!

Michael Richey

Locale: Southern Utah
mad scientist on 01/05/2010 21:09:33 MST Print View

Your mad scientist characteristics are what really set you and your reviews head and shoulders above the rest of the reviewers! Keep up the quantifiable differences!

Mary D
(hikinggranny) - MLife
Marmot Hydrogen Sleeping Bag Review on 01/06/2010 00:17:54 MST Print View

I bought a Hydrogen five years ago. It was black, not that awful vomit green! The problem was that for shoulder-season camping, it just wasn't warm enough! I put on all the insulating layers I had inside it, and I shivered the whole night (25*). I sold the Hydrogen and bought a Western Mountaineering Ultralight Super, and have never regretted it!

Stephen Barber
(grampa) - MLife

Locale: SoCal
Hydrogen for Christmas on 01/06/2010 08:47:26 MST Print View

My wife just gave me a Hydrogen for Christmas - looks like she choose well!

Dave -
(FamilyGuy) - F

Locale: Up there
Marmot Hydrogen Sleeping Bag Review on 01/06/2010 08:58:25 MST Print View

Nice bag. But for me, being of the wider sort, the MB would work better. Given that I carry a Cocoon Hoody anyway, I could just layer in to push the temps. 1/2 a pound difference and almost $100 is significant given that there is the option of using gear you are already carrying to increase warmth.

Mark Keown
(aarnbodypacks) - F

Locale: NZ
Hydrogen on 01/06/2010 13:04:01 MST Print View

What accounts for the curves crossing at about 11:40? It looks like for the first hour the 125F water is heating up the tub and sensors. But if the Hydrogen is loosing heat slower it should of heated up the gear quicker. Is there a thermoconductivity change with time or temperature?

Mike M
(mtwarden) - MLife

Locale: Montana
hydrogen on 01/07/2010 18:41:34 MST Print View

I purchased a Summerlite reg. and while the weight was certainly attractive, it was just too tight for me (6' 200#)- I ended up trading it with a member for a Hydrogen reg.- I think we both ended happy :)

Johnathan White
(johnatha1) - F

Locale: PNW
Hydrogen on 01/08/2010 15:02:51 MST Print View

Great write-up Will!

I have 3 Marmot bags and hate the fact they axed the Pertex Quantum they previously used. I remember using the Lithium with the P.Q. and woke up with a puddle over my chest, and ice from the gut down and the fabric was bone dry without a hint of wetting through.
I had my daughter's cat make a play-toy out of my 0-degree Lithium and had to send it in to be repaired only to see patches made of the ghastly new fabric.

Will Rietveld
(WilliWabbit) - MLife

Locale: Southwest Colorado
Responses to Marmot Hydrogen Comments/Questions on 01/10/2010 08:24:45 MST Print View

Hi all, thanks for your comments. Here are some individual responses:

David: You're right, a better comparison would be with the WM MegaLite. I was thinking in terms of the lightest bags and overlooked the MegaLite as being a closer comparison. Sorry for that. Weight-wise, the MegaLite is the same as the Hydrogen.

Mark: Good observation on the curves crossing. I don't have an explanation and am still thinking about it. I ran the test twice and got similar results, so something is causing the difference in warm up. For my State of the Market report on UL 3-season down mummy bags, to be published this spring, I plan to run comparison tests using a regulated heating pad inside, and maybe that will work better. It will be a "poor man's mannequin test" to produce some Relative Warmth data, similar to Richard Nisely's tests.

Best regards and happy hiking,