Dreaming of Mountain Nights, Getting to Know the Rab Mythic Ultra Sleeping Bag

Normally, I’d hope to be spending some nights up on a mountain.

Dreaming of that, I finally bought a sleeping bag that should be great – and we can, at least, have a look at the construction and technology of it, the Rab Mythic Ultra 360.

Rab has a long history of producing gear for the mountains, and especially with sleeping bags.

The Mythic Ultra, available in a lighter 180 and the heavier/warmer 360 version I got is their latest-and-greatest at this time (2020).

The Basics

The Rab Mythic Ultra 360 weighs in at 606 grams, but its temperature rating goes down to -27C (-17F) in the extreme.

The comfort rating is -2C (28F); the ordinary limit lies at -8C (18F).

Rab Mythic Ultra Temperature Rating
Rab Mythic Ultra Temperature Rating

This is the rating after the EN standard, using a thermal manikin and measuring its heat loss, though – and according to Rab, this does not take into account the effect of their TILT technology (see below).

In spite of (or actually, because of!) the fill that lofts the bag up tremendously – it’s a 900-fill power European goose down, after all – the bag compresses to a very manageable volume.

Dry Bag and Packing

The dry bag that comes with it should be around 3-4 liters in volume. Rab calls it a “compression stuff sack,” but it lacks any extra straps for compression. Rather, there is only a, dry bag-typical, roll-top closure.

(It’s still a nice bag, though I’d wish for a little more compression, given that I’m not only looking for light weight, but also low-volume, since I aim to travel fast and with a -rather- small backpack.)

Rab Mythic Ultra, packed (and left to extend in its carry bag) with Neo Air mattress and Lowe Alpine Uprise 40:50

Storage Bag

For storage, by the way, the sleeping bag also comes with a cotton bag; even that has a nice simple pull-loop and carry strap on the opposite side of the opening.

The (Highest) Standard of the Bag

The Mythic Ultra is already high-end in its use of a very soft-feeling “super lightweight 7D” ripstop nylon shell and liner, 900-fill power European goose down with Nikwax hydrophobic treatment, and excellent construction.

Shape and Baffles

The build is quite a typical mummy shape, with angled foot box, a cut throughout that is shaped along body contours.

Chambers/baffles are trapezoidal in construction, as Rab usually does them. This is meant to ensure that the down stays in place while air can circulate (and move out when packing the bag down) through the mesh forming the baffles, and to prevent any cold spots at seams.

The hood is, of course, made with a draft collar, which is pretty substantial.

Rab Mythic Ultra Hood and Collar
Rab Mythic Ultra Hood and Collar


The collar shapes around shoulders and neck very nicely (not just straight, but with a bit of a curve to follow the sleeper’s body). Rab speaks of an “ergonomically designed internal collar and hood.”

What I am not yet sure about is how well the elastic drawcords for hood and collar are going to work and hold up; they seem to have to extend (get stretched) very far into the bag to cinch tight.

I wonder how well this will function. Then again, as substantial as the loft of the bag is, it may not even be necessary to draw it closed too much.


Entrance/opening of the bag is via a left-hand zipper.

If you don’t just climb in through the top opening, which extends wide enough for that (and may be the way to climb in if just using a minuscule bivy – I’m thinking of the Outdoor Research bivies I’ve been using or even smaller ones).

The zipper goes down to hip-height, where there is also a second pull in case you feel a need to get some additional ventilation.

All along, there is a baffle/collar at the inside of the zip to keep out any potential drafts.

Rab Mythic Ultra Zipper Garage
Rab Mythic Ultra Zipper Garage

The top of the zip also has a sizable flap to use as a zipper garage; the bottom ends a bit abruptly (making me a little concerned it might be possible to unhook the zipper pull – though I think I’m just too worried here), but the two halves of the bag are nicely connected inside.

Of course, the zipper pulls can be moved inside as well as be on the outside; the top one also has a drawcord extension to be more easily found and gripped – and the puller on that is noctilucent, i.e. glow-in-the-dark, to boot.

There is a lot of material – or rather, light and airy as it all is, it looks like a lot – everywhere, but my playing around with the bag has not found the zip snagging, so far.

Nikwax Hydrophobic Down

900 fillpower hydrophobic down being used throughout the bag means that this bag lofts up very nicely, giving it its insulating power that protects against cold night temperatures.

Thanks to the hydrophobic treatment from Nikwax, this down can handle wetter conditions much better than traditional, untreated down could.

The Problem with Down

Down is great at insulating – but only as long as it does not get wet.

On birds, their down is protected by the feathers – but water birds have to regularly ‘treat’ their feathers with a secretion or they would not repel water!

The down in and of itself, and cleaned as it has to be for use in a sleeping bag, takes on water, clumps together, loses its loft, and becomes very uncomfortable to sleep in.

That has always been the problem with down sleeping bags: They are much lighter and more efficient than synthetic bags – if the weather is dry. And if you don’t sweat into your sleeping bag.

The Nikwax Solution

With Nikwax Hydrophobic Down, the down “can resist 16 hours of direct exposure to water and still retain it’s insulating properties,” to quote directly from them.

This is not only interesting for rainy days (and nights), but also for the sleeping bag to – hopefully – perform well if sleeping hot and sweating, if there should be condensation buildup in a tent or bivy, etc.

Rab Mythic Ultra TILT
Rab Mythic Ultra TILT

The Mythic Ultra’s Special TILT

What sets this sleeping bag apart from others is that it is not only using some of the standard best production, but has been given a special, uhm, TILT…

The liner also uses “Thermo Ionic Lining Technology” (see, TILT).

How you can see that? It looks like the reflective textile linings that are in use in some clothing, mainly jackets.

What does it mean? It means what is known from such clothing – the lining is treated with metal ions (titanium, in fact) that are meant to reflect warmth from infrared radiation that your body emits back to you.

Rab Mythic Ultra TILT Liner
Rab Mythic Ultra TILT Liner

So, Like an Emergency Blanket?

I’ve seen people wonder why, then, we don’t just use reflective emergency blankets in our sleeping bags.

Well, of course, because those crinkle and are noisy and would mean sleeping like a baked potato in the oven.

Through the TILT, the metal is made a part of the fibers.

The breathability should still be good (this is one of the things I’ll want to look at when I can put the bag to practical tests).

And the feeling is not metallic or crinkly at all. The bag is soft and comfortable all around!

Comfort – and Higher Performance – To Test

In effect, with TILT, there is not only the heat retention – of body warmth – from the air trapped in the insulation layers, i.e., in the down filling of the sleeping bag (which is what the ratings according to EN/ISO standard stated at the beginning of the post are based on).

There is also the heat reflection – of IR (infrared) from your body – kept in by the ions in the lining. This should extend the temperature capabilities of the sleeping bag still further!

At the same time, breathability is also kept high – and the hydrophobic down should do its part in regulating humidity, and keeping the bag functioning.

Now, to get back into the mountains, see how the bag packs, fits inside my backpack, works with the bivy…

Disclosure: This post is my own editorial content; I did NOT receive this sleeping bag from the producer, nor even a discount; I simply bought it myself.

Following is an affiliate link, though, so if you make a purchase through this link I (may) get a commission from your purchase.

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  1. Martin

    Seems like a great sleeping bag! So I understand it’s very efficient when it comes to the weight-warmth ratio but how about packed volume? Is it great in that aspect also? Is it possible to compress it a lot if I buy a third party compression bag or is it limited margins for compression? Thanks a lot in advance!

    • It comes with a much smaller bag (not compression, but roll-top) that it can be pushed into; and it packs down *pretty* small for the loft it has.

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