The holy grail of sleeping bags is a mythical beast, oft spoken about in dark corners of gear shops & around the campfire on cold dark nights in the mountains… OK, I’ll get to the point. Everyone would love that one sleeping bag that, put quite simply, does it all. I definitely would. Sadly, to the best of my knowledge, a single sleeping solution for all life’s outdoor adventures does not yet exist. How can one sleeping bag possibly cater for your summer trekking trip deep into the jungles of Borneo, then still cut the mustard for a winter expedition in the Karakorum? It just can’t.

But don’t worry, there is still hope! How about a sleeping bag that is versatile for most of your cold weather adventure needs? The newly released Sea to Summit Latitude Series of sleeping bags aims to be just that, one bag that is versatile enough to not only be suitable, but excel in a wide variety of scenarios. There are three options of Latitude (Lt) available and instead of trying to list all the specs & features, I’ll refer to this wonderful chart Sea To Summit have prepared to simplify things.

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Technical Wizardry:

The bag I’ve been using is the Latitude LtIII. [Note: the one I’ve reviewed is actually pre-production sample that is identical to the production sleeping bags, apart from a slightly different shade of fabric used on the outer shell. The new green colour is much nicer in my opinion anyway! ] As you can see the Lt III is the warmest in the line-up. STS give it a Comfort rating of -10°C, with a Lower Limit rating of -17°C. What does this translate to in real world ‘how warm is it really?’ terms you ask. Basically a normal sleeper will have a comfortable nights sleep between these two temperature ranges. Someone who feels the cold would be OK down to around -10°C, whilst a warm sleeper may be comfortable down to approximately the -17°C mark. These ratings are only a guide & subject to several other factors. If you’re unsure how best to get the most warmth from your sleeping bag – have a read of our How to Sleep Warm article. Likewise If you’re a bit confused about how all this mumbo jumbo works, check out Sleeping bags 101 also on the blog this week.

Down Technologies. So it’s a warm bag, OK thats good! But how well does this thing squish down? The Latitude bags use 750+ Loft ULTRA-DRY Down™. In layman’s terms, the 750+ down fill used sits the upper-to-middle region of what’s available. Cheaper bags might use 550 – 650 Loft down, whilst high-end bags will Use 850+ Loft. Essentially the higher the loft, the greater the warmth-to-weight ratio of the insulation, & by extension you will pay higher price. The down used in the Latitude is also treated with a water resistant coating. This serves multiple purposes, but the most important is that it keeps the bag drier longer. Down insulated gear is basically useless when completely saturated. The drier your down sleeping bag is, the better. The ULTRA-DRY Down™ treatment is a durable Nano-level water repellent polymer treatment applied to the down. The treatment improves the down’s reaction to water without effecting its weight or loft performance. Sea To Summit claim that compared to untreated down, their ULTRA-DRY Down™ retains over 60% more loft and absorbs 30% less moisture. This also means when your Sea to Summit sleeping bag gets wet, as it inevitably will do at some point, it will dry out much faster than bags with untreated down. Other advantages of the treatment include enhanced anti-bacterial and anti-microbial properties, thus less cleaning required. Always a plus in my book!

Construction & Fabrics. The latitude is constructed using a side block baffle construction. This means that the down baffles (chambers) are separated between the top & bottom of the bag. This design enables the bag to maintain a 60/40 down fill ratio for maximum insulation, but it also eliminates ‘down migration’ or cold spots. See below for a diagram illustrating this style of baffle construction.  The outer shell face fabric of a sleeping bag is another crucial element in the overall design. The Latitude uses Sea to Summit’s 2D NanoShell™, which is a 20 denier Nylon rip-stop with micro-porous coating and treated with a DWR finish. Inside the bag you’ll find a 20 denier Polyester with a soft touch hand feel. To help regulate temperature this material is breathable, but also light and incredibly durable for its weight. Both the shell & lining fabrics are also a high density weave, which helps make them more ‘down proof’, thus reducing the likelihood of down escaping from within the bag.

Cut & Features:
A big part of what makes the Latitude so versatile is the cut & zipper design. The bag has been designed with a Technical Tapered Rectangular shape, so basically it’s not a super trim mummy bag, but its more compact & tapered than a full-on rectangular cut. The result is a comfortable, unrestricted sleeping chamber that’s still trim enough to be quite thermally efficient & pack down very small. I’ve been using a variety of narrow mummy bags for years & the spacious cut of the latitude was actually a welcome change. There are two overlapping zippers running down one side & along the foot of the bag, which allows you to open it right up into ‘doona mode’. Or if you’re overheating just a touch, simply open one or both of the zippers to allow a bit of venting.

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The Hood of the Latitude is very well thought out. It’s big & well shaped, but still cinches in close for those really cold nights. There’s a sizable down filled neck baffle that you can cinch with a separate elastic pull, designed to stop that unwanted 5am chilly winter draught from disturbing your beauty slumber. You’ll even find even a handy internal storage pocket for electronics like your phone, batteries or headlamp.

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Size & Storage.
Sea to Summit list the compressed & uncompressed volume of each bag, but to put that into perspective I’ve taken some shots of the Lt III, firstly puffed in all it’s glory, then squished in the included compression stuff-sack. (Note: Always store your down uncompressed whenever possible, especially for long periods of time). All latitude bags include an appropriately sized Sea To Summit Ultra-Sil stuff sack, plus in the case of the Latitude, nifty newly redesigned & expandable storage cube/sack. To give you an idea on just how puffy this bag is when lofted, whilst staying in a back-country hut in NZ, I came back from a day excursion to find some new arrivals. Someone had been so convinced there was someone sleeping soundly in my bulging Latitude during my absence, that they gave it a gentle prod, after failing to rouse the imaginary occupant by saying hello. It’s that fluffy!

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Sleeping together for 3 weeks.

I’ve just returned from 3 weeks of alpine climbing & trekking on the South Island of NZ. My sleeping accommodations varied from open rock bivouacs & sleeping in a tent, to staying in back-country huts. There was even plenty of rain & moisture thrown into the mix, to really make it exciting. The latitude was the only sleeping bag I took on this trip, so it had to do everything. But how well did it fare you’re wondering? Well in short, I loved the bag.

Lets start with the least challenging terrain, a nice comfy bunk in a cozy hut. The huts I stayed in during this trip were all pretty nice, large with big solid timber bunks & thick foam mattresses. They were mostly coal/wood stove heated too, so the latitude started to get pretty warm some nights. I just un-zipped the bag completely and settled under nice warm, albeit much more breathable doona/quilt. The lowest temps I experienced in the huts was about 5°C, so not cold, but definitely cold enough to warrant a decent sleeping bag. Having a nice warm bag to wrap myself up in whilst waiting out some torrential rain at Dart Hut for three days… the Latitude was excellent. Especially when my tea supply ran low towards the end of the trip. 

Enjoying a cozy afternoon reading in Dart Hut, whilst the rain poured (for 5 days straight!) outside.

So how’s it go outside you ask? Say in an Open bivvy in an alpine environment. During the first half of my NZ trip a couple mates & I attempted some walk-in alpine peaks. Sleeping out & as close as possible to the base of the climb was required. The colder of the two trips was Mt. Brewster. Our bivvy spot was at about 1900m elevation & clear star-filled nights made for excellent conditions to sleep out in the open. I was curious to really test the Latitude so slept on top of my bivvy the first night. In the morning there was some moisture gathered on top of the bag, but surprisingly not much had soaked in. Throwing it on a rock in the sun was all that was needed to dry the small amount of moisture that had penetrated the top of the bag. More importantly, the loft appeared completly unaffected.The second night of that trip was colder, dipping below zero. I decided to jump inside my eVent bivvy sack this time, but found despite the sub zero temps i was still oppening the side vents, feeling cold was not an issue! On another occasion, after 10 hours of torrential rain/sleet/snow & a very cold chest deep river crossing – I pulled the Latitude out of it’s stuff sack to find it a bit wet around the hood (Almost everything was a bit wet…). I just threw it over a bench near the coal-burning stove & it was dry in time for bed an hour later. Of course the best option is always to keep your sleeping bag dry, but good to know that it will handle some moisture if needed.

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[L] Cooking dinner from inside the Traverse & [R] letting the bag dry out a bit in the morning, both at our bivvy spot below Mount Brewster.

I also used the Latitude sleeping in a tent a few times, specifically my little Nemo Tenshi 2p which is a single skin alpine tent. The Nemo is great, but given that it’s designed for use in alpine/snowy/cold environments, I chose to sleep with the main door & all vents open. It was in cold, but well below the tree-line so still quite moist. This minimised any condensation build-up inside the tent, but also allowed some dew to settle inside on my exposed bag overnight. I was super toasty despite the mercury dropping below freezing again. As to any moisture, I didn’t realise until the morning, as the warmth was not affected. Again a win for DWR treated down & water resistant fabrics.

Initial Conclusions:

In summary I think the Latitude is a great sleeping bag. The adaptable design allows it to not only be used in a variety of situations, but not compromise factors like warmth & weight. Sure there are ultra-high loft narrow mummy bags around  that will weigh less, but they could cost you twice as much. Likewise, a big feather doona would be nice in the hut… Ok that’s a bit of stretch. Throughout the trip my sleeping temps only dropped a bit below freezing, so I didn’t get a chance to really see how warm the LtIII could be. I actually had the foot & side zips partially open on the coldest nights as it was too warm! My best guess is that if you stick to the temperature guide Sea to Summit has made, you’ll be fine. I’m likely heading to the snow again this winter, so am looking forward to testing out the Latitude in some really cold temps. In the meantime, it’s summer here in QLD, so time to put away my big green caterpillar & dream of cooler climes.

If you’re looking for a quality, lightweight, warm & versatile sleeping bag definitely check out the Latitude. Not convinced it’ll pack down small enough, try one out in store. Same goes for the roomier cut, jump inside the freedom of movement for yourself.


Settling into my bivvy at the head of Gorilla Stream, Aoraki/Mount Cook National Park.

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Review: Sea to Summit Latitude Sleeping Bag
Weight & Compressability80%
Design & Features90%
Value for Money90%
  • Warm & cozy which is the most important factor
  • Versatile & adaptable to a variety of sleeping situations
  • Great weather/mositure resistance, especially given the lightweight construction/fabrics
  • Not the lightest bag for its warmth
  • Only comes in green?
88%Overall Score

About The Author

Lachlan Gardiner

Lachlan works as a freelance photographer, writer and videographer. His practice lies somewhere between storytelling and being a total gear nerd. Often found hiking, mountaineering, climbing, cycling, packrafting, or just hunting down the next story - Lachlan will take basically any excuse to get into the outdoors. In between all of the above, he also works in our Paddy Pallin store in Fortitude Valley, Brisbane.

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