Marmot Hydrogen Sleeping Bag

The Hydrogen Sleeping Bag
© Marmot

A Down Feather
Sleeping bags: Down or Synthetic? Warm or light?

These are questions you need to ask yourself before you buy a sleeping bag. The answer will vary depending on what you want to use your sleeping bag for.

You want a 'do everything' sleeping bag? So do I! However, a bag that keeps you alive in a Himalayan storm is also unlikely to be comfortable when you're bivvying at Cloggy on a warm September evening. They are all tailored to a specific temperature range. The heavier the sleeping bag, the warmer it will be. Look for a sleeping bag that has a temperature rating that suits your chosen activity.

The big question: Synthetic vs. Down:

Sleeping bags are filled with insulation – that's the fluffy stuff that keeps you warm. This insulation is composed of either man-made 'Synthetic' fibres or 'Down'. Down is basically feathers.

Down packs smaller and weighs less than an equivalently warm amount of synthetic material. Also good quality Down lasts longer than its synthetic counterpart. So Down is better? Only if you keep it dry. When soaked, a Down filled sleeping bag will lose most of its insulation properties, whereas a synthetic bag will stay warm. So the answer is simple:

  • Going to get wet? - Go for Synthetic
  • More concerned about weight and bulk? - Opt for Down

Okay, as the Hydrogen is a down sleeping bag, we'll assume that Down was our first choice, but is all Down the same? No. Down insulation is rated by fill power, measured as the number of cubic inches displaced by a given ounce of down (in3/oz). Higher fill-power downs will thus insulate better than lower fill-power downs of the same weight.

The Marmot Down Fill rating - 850!
From Wikipedia:

"Fill power is a measure of the loft or "fluffiness" of a down product that is loosely related to the insulating value of the down. The higher the fill power the more insulating air pockets the down has and the better insulating ability. Higher fill powers are associated with a larger percentage of down clusters and a larger average down cluster size. It involves measurements taken of a one ounce sample of down in a plexiglas cylinder with a weighted piston compressing the down. The test requires controlled temperature, humidity, and preparation of the sample. All other things being equal a parka (duvet or sleeping bag) made with high fill power is lighter and more compressible than an equally warm one made with lower quality down. Fill power is expressed as cubic inches per ounce (c.i/oz) -- a lofting power of 400-450 is considered medium quality, 500-550 is considered good, and 600-700 is considered excellent."

What to look for in your Down

  • A high fill power: Means that the bag will be warm for its weight. Anything above 700 is top-notch. You can see from the photo on the right that the Marmot Hydrogen has a fill power of 850, this is really superb.
  • Type of Down: To get extremely high Fill Power, only the finest feathers can be used - meaning that they are taken from older birds. So if you opt for a high fill-power bag, you know you're getting the high quality down.
  • Make sure the fill power rating is accurate: Sleeping bags are often sold with a temperature rating, this is nothing to do with fill-power. Some high fill-power bags will be colder (but much lighter) than a heavier bag with a lower fill-power. Fill power is about warmth and weight. Fill-power can be tested by professionals and a good quality manufacturer will get their product certified. The Marmot Hydrogen is tested and certified by International Down and Feather Laboratory in Salt Lake City, Utah.

Madagascan Big Walling - Tiring Work.
Temperature Range:

We've chosen Down. We've looked for the highest fill-power and we understand Down. We need to choose the right bag. The Hydrogen is rated thus:

Comfort: 39.2F / 4C
Transition: 29.84F / -1.2C
Risk: 1.04F / -17.2C

This means that an 'average adult female' can sleep comfortably in 4C temperatures and an 'average adult male' can sleep comfortably in -1.2C temps. It should keep the same 'average adult male' from freezing to death down to -17.2C in an emergency. (Women in general sleep colder than men - hence the two ratings). Do not expect to be snug and warm at -17, this is for survival purposes only!

This is a good temperature range for Alpine summer climbing, UK camping and general use. It isn't designed for high altitude mountaineering or for Alpine winter use.

The temperature ratings are only a rough guide. Lots of variables will affect how warm you feel inside your sleeping bag. Did you eat enough food? Are you dehydrated? Did you get your sleeping bag damp? Are you drunk? A little bit of experience of sleeping at different temperatures will soon tell you whether you sleep warm or cold.

Weight was an important factor big walling in Madagascar

Sleeping in the van on a recent UKC business trip (photo Mick Ryan)
Is the Marmot Hydrogen any Good?

It fits our needs; the temperature range is right and we want a Down bag not a Synthetic one. So is the Hydrogen a good choice? YES!

I've used the Hydrogen bag camping in the UK, sleeping in my van with Mick Ryan on very important business meetings for UKC, on a camping trip to Europe and an extended trip big walling in Madagascar. The shell is made from 'LightForce N-120R DWR' (whatever that means) and is tough and extremely light. I've slept in prickly Madagascan bushes and the fabric has stayed intact. The inner fabric is very similar, but perhaps a little softer on the skin. Again I have had no problems after several months of hard use.

We have already established that Marmot have used exceptional quality Down in this sleeping bag and it has stayed lofted and 'puffy' even after repeated cramming in to a stuff-sack. I haven't had to wash the sleeping bag at all (washing correctly can help re-loft old bags). The zip is a high quality YKK zip, which has worked perfectly and felt sturdy. The fabric of the zip baffle has occasionally got stuck in the zip, but is more than tough enough to cope with being trapped and has always easily come out unscathed. Marmot have added a 'Zipper Guard' to stop the zip from snagging - this is a stiffened section of fabric behind the zip. It did work to a degree, but as with all sleeping bags, they do get snagged occasionally.

The shape of the bag is well thought out. The hood design is pretty much perfect and covers the head snugly, trapping in warmth. The baffle is great - well designed with no velcro or other rough materials that might irritate your face during sleep. Equally the zip hides away under the baffle nicely and doesn't rub your chin. The foot box is shaped ergonomically too, meaning your feet have enough room (even my size 10 boats).

The draw-strings are in the right places, easy to reach and work well. The colour, well it's kind of a shiny green. I think it looks quite smart, but you'll have to make your own mind up.

Pack Size
Weight: According to my trusty Tesco kitchen scales the Hydrogen comes in at a tiny 712g, which is the same as 2 apples and a banana. Not bad!

Pack Size: See photo on the right.

Conclusion: A super-light summer Alpine or UK bag, with all the features you need, none that you don't. Well made from the finest materials with great, simple design. If you are looking for a down sleeping bag for bivvying in the Alps, general UK climbing/camping use, lightweight backpacking etc then this would be a good choice. If you're looking for a winter Alpine bag or something for bigger mountains further afield, then look for something a bit meatier.

More info on the Marmot Website

Construction Detail
© Marmot
Info From Marmot:
Weight: 1 lb 9 ozs / 709 g
Main Material: LightForce N-120R DWR
Lining Material: LightForce P-100 DWR Taffeta
Insulation Material: 850+ Goose Down
Size for stature: 183 cm
Size on shoulder: 157 cm
Size on hip: 147 cm
Size on foot: 102 cm


  • Certified 850+ Fill Goose Down
  • Classic Trapezoidal Foot Box For More Foot Room
  • Full-length Zipper
  • Hood Draw Cord Positioned for Easy Access
  • Insulated Draft Tube Eliminates Cold Leaks Through the Zipper
  • Stretch Tricot Baffles Provide Ultimate Strength, Durability and Bag Life
  • Stuff and Storage Sack Included Store and Pack Just Like Your Sleeping Bag
  • Velcro®-free Face Muff Keeps the Drawcord and Zipper Away from Your Face
  • Zipper Guards Help Repel Biting Zipper Coils

For more information visit Marmot Website
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