Mountain Equipment Helium 400 sleeping bag review

Why the Mountain Equipment Helium 400 is my go-to sleeping bag

The Mountain Equipment Helium 400 solves the problem of what to buy as a genuine three season down sleeping bag for Britain. The bag is, you guessed it, filled with 400 grammes of down. This is the same as many other sleeping bags, but the Helium 400’s superior design makes it warmer.

What is a 3 season sleeping bag for?

This is hard to define and varies from country to country. I am talking about the British isles or similar climates. It should be capable of keeping you warm when temperatures are around freezing but not much lower. This means it is a lightweight sleeping bag you can use on all but the coldest winter trips. If you only have one bag and want to camp in late autumn and early spring, this is the one to have.

Pricing of the Helium 400

The Helium 400 retails at around £240, which is more than many three season sleeping bags. The Rab Ascent 500 is cheaper at around £200. A great value alternative is the Alpkit Pipedream 400 at £215.

Is the Helium 400 good value for money?

My wife has the Pipedream 400, which cost less than the Helium 400, but it’s not as warm or comfortable. The Helium 400 works well at sub-zero temperatures and the Pipedream 400 doesn’t.

What you are paying for is the design of the Helium 400. It’s in a different league to its cheaper rivals. As a result, it delivers superior warmth. That makes it worth the extra money to me.


The Helium 400 is made from 100% recycled fabrics.

All the baffles in the main section of the bag are a slanted box section, which means the down doesn’t have thin spots where the seams are. This contributes to the warmth.

There is a 3/4 length zip that is snag free and well baffled. The zip area is not cold.

You can find the full spec on Mountain Equipment’s website:

Design features of the sleeping bag

The complex hood and neck design of the Helium 400 is excellent at keeping the heat in. If you want a true 3 season bag, then this is critical. Heat lost out of the hood and neck will rapidly make you cold. This is not an issue in the summer, but if you want a bag that still keeps you warm at -1, it needs to be considered.

The hood

The hood comprises 5 separate sections, which make it fit snugly all round the head and neck. This makes it extremely comfortable and warm. The comfort means I actually use the hood. On other bags, I try not to put the hood up as I find it restrictive.

The hood has 2 draw strings that are adjustable from inside the bag. They both share the same locking device but are 2 separate strings. One goes under your chin and the other around the top of the hood. Being able to adjust these separately is a plus. They are very easy to operate.

The hood cord is distinguished from the neck baffle adjuster by being string as opposed to elastic. This is a clever design and saves a lot of confusion.

The neck

The neck baffle is one of the best features of the Helium 400. It is a critical thing to get right if you want to be warm in freezing conditions.

The baffle is an 8cm diameter tube that encircles your neck. It comprises 2 separate sections that are well filled with down. It’s easy to distribute the down how you like it. The down stays put and doesn’t clump up.

There’s a nifty magnetic clip at either end of the baffle. The two magnetic parts seek each other out as soon as you zip the bag up. You hear a satisfying click as they join. This stops warm air leaking out and is a significant reason why this bag is warmer than others.

To undo the clip, there is a webbing tab that has a raised embroidered circle on it. A gentle tug on this and the neck is undone. This attention to detail makes the Helium 400 stand out from the crowd.

I dread to think how much research and trial went in to this catch. But it was worth it. It’s not a gimmick, it really works, and makes a big difference.

The foot end

The shape of the foot end is tapered in two directions and fits snugly around my feet and keeps them warm. It comprises 4 separate compartments, and the down distributes well with no cold spots. A lot of thought has gone into the design and it pays off.

The down

The down is duck and rated at 700FP +. It bucks the trend and doesn’t have a hydrophobic treatment. This concerned me, but the words of Dr Down at 13 minutes in this video reassured me.

Mountain Equipment addresses the question here:

Marketing hype surrounds the whole goose/duck and hydrophobic thing. Once you see through this, it is clear hydrophobic duck down is not inferior. In the real world, the Helium 400 proves this. It’s warmer than my goose down bag and has no smell.

The “Down Codex” provides a serial number for the down and you can look up where the ducks came from. And what the fill power of your specific batch is. Mine is 750FP. Mountain Equipment sources the down ethically, and they can prove it.

How comfortable is the Helium 400?

This is a warm and very comfortable sleeping bag. Not too big and not too small. The hood fits well and doesn’t feel restrictive. The bag stays with me when I roll over – so does the hood. I have not known another bag to do this so well.

How warm is the Helium 400?

The bag has a comfort level rating of 0 degrees C and a comfort limit of -6 degrees C. I have slept in it at -1 and was extremely warm.

I have also experienced the Alpkit Pipdream 400, which has a -4 degrees C comfort rating with a comfort limit of -10 degrees C. It didn’t keep me warm at -1.

The Alpkit bag has a pretty basic hood design and a very minimal neck baffle. Could this be the difference between 2 very similar bags?

On paper, the Pipedream 400 is the warmer sleeping bag. But in the real world, the Mountain Equipment bag is warmer. They both contain 400g of 750fp down, but the design of the Alpkit bag is inferior. I can only assume this is why it is colder than the Helium 400.

Weight and size of the sleeping bag

At 183 cm, I find the regular sized bag exactly the right size. The length is perfect and for my slim build, it’s not too wide. It finds the right balance of efficiency and space to manoeuvre. There is also a long version.

Weight: 820g

Standard Pack Size: 24cm x 21cm x 20cm

Accessories that come with the Helium 400

The Helium 400 comes with a storage bag that is well ventilated and is a cube. I’m not sure of the point of the shape, but it does the job.

There is also a dry bag that has an interesting feature. An eyelet in the roll up section to expel air when it is being rolled up. To my mind, this is pointless and is trying to solve a problem that doesn’t exist. The dry bag leaks air and expands, which may be to do with the eyelet. I don’t use the dry bag for this reason. I continue to use my Osprey one.

Alternative sleeping bags

An obvious competitor is the Pipedream 400 from Alpkit, which I also own. Another is the Rab Ascent 500. This was the bag I first looked at as I already own the Ascent 700 and love it. It is bigger and heavier than the Helium 400. If I didn’t already own the ascent 700, I would have gone for the Ascent 500 as it is slightly warmer on paper than the Helium.

There are also technical and lighter bags for a lot more money. For 3 season use in the UK, these sleeping bags are over the top.

Why I love this sleeping bag

It’s the minor details that make the Helium 400 a brilliant bag. They all add up to create a sleeping experience that’s hard to beat.

At the end of the day, literally, it comes down to how well you sleep. And I sleep better in this bag than any other I’ve owned. Summer or winter it’s the bag I turn to. It’s only when it’s going to be minus several degrees that I use the Rab Ascent 700.

It’s more expensive than some other bags but it delivers a lot in return for the money.

If I only owned one sleeping bag, it would be the Helium 400. It can be used most of the year and eliminates the need for a bigger, heavier bag in spring and autumn.

The Helium 400 is small, light, and warm, which is what I want from a sleeping bag. The neck and hood design is brilliant, which means the bag works below zero. That’s hard to achieve in a 400g bag but Mountain equipment has pulled it off.

Highly recommended.

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