Sea to Summit Alpine Sleeping Bag Review -1 Degree Field Tested

When it’s bitter cold out and you want to keep hunting, having the right sleeping bag is critical. Enter this Sea to Summit Alpine sleeping bag review. While many of us may shy away from spending nights in a tent when temperatures drop below zero, if you have the right equipment, it really can be very manageable, even quite enjoyable.

I was able to test out this Sea to Summit Alpine Sleeping bag over this last winter and came away very impressed with just how warm it was. While I was “only” able to find temps down to -1 degrees Fahrenheit it’s no surprise that this Alpine -40 (-20 comfort rating) kept me toasty warm. What was more impressive though, was just how warm I was, as well as the design and layout of the bag. We’ll get into that more below.

The Sea to Summit Alpine sleeping bag comes in two different models; a -5 and a -40 degree version. The -5 features a “lower limit” rating of -5 and a “comfort” rating of 10 degrees, while the -40 model features a lower limit of -40 degrees and a “comfort” rating of -20. In my extensive experience testing sleeping bags, not all bags out there even come close to their advertised ratings, so I like how Sea to Summit gives you a comfort rating which tells you what temps you should realistically be warm in.

Sea to Summit Alpine Sleeping Bag Specs

Sea to Summit Alpine Sleeping Bag Review

The Sea to Summit Alpine Sleeping bag boasts some really impressive specs, particularly for the warmth you get. Coming in at just 2 lbs 15 oz for the -5 degree model, and only 4 lbs 2 oz for the -40 degree model, you’ll be kept warm in a lightweight package. Here are some of the other specs for the Sea to Summit Alpine Sleeping bag:

Sea to Summit Alpine Specs (Reg Length & Width)
Model -5 Degree -40 Degree
Weight 2lb 15oz 4lb 2oz
Packed Size 9.3L 14.7L
Down Fill 28oz 44oz
Sizing Expedition Expedition
Shoulder Width 63in 63in
Shell Material Water Repellent Nano Shell Water Repellent Nano Shell
Down Insulation 850fp RDS Water Repellent Goose Down 850fp RDS Water Repellent Goose Down

The Sizing: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

The Sea to Summit Alpine Sleeping bag comes in an “Expedition Sizing” as to allow plenty of space for layering while using it. With that being said, I didn’t find it to be oversized at all. I would describe it as a comfortably roomy mummy bag, but not too large to be inefficient. There is enough room to move around comfortably, but it’s still pretty snug. When zipped all the way up, it takes a little maneuvering to get it unzipped or zipped back up, but that’s what helps make this Alpine sleeping bag efficient and super warm.

Extra space in a sleeping bag is just dead air your body has to heat, so minimizing that while maintaining comfort is a trick, but it ultimately comes down to personal preference. If you can handle a true mummy bag, they are the most efficient but extremely restrictive. Personally, I can’t do a mummy bag, but found this Sea to Summit Alpine to be the perfect blend for me. Not too big, but not so small that it restricted movement.

The Weight: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

When it comes to a cold weather sleeping bag, weight becomes less of a concern. I’m simply not willing to compromise being warm for saving a few ounces when dealing with sub zero temperatures. That said, the beauty of the Sea to Summit Alpine sleeping bag is that you don’t have to compromise at all. At just 2 lb 15 oz for the -5 degree model and only 4 lbs 2 oz for the -40 degree model, you can stay extremely warm while keeping the weight to a minimum. As with any cold weather gear, it starts getting bulky, and the -40 degree model I tested certainly takes up a good chunk of real estate in your backpack at 14.7L.

However, I was able to manage taking the Alpine Sleeping bag for a long weekend hung along with a Seek Outside Cimarron tent and one of the Seek Outside SXL Titanium stoves in my Initial Ascent IA4K backpack without much trouble. Sure, bringing cold weather gear for temps dropping to the single digits overnight fills up a 4k pack, but it was doable. Man, what a game changer it was to have a hot tent like the Seek Outside Cimarron! If you haven’t yet, check those out!

Warmth: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

Warmth was one of the critical tests for this Sea to Summit Alpine sleeping bag review. It’s often where good sleeping bags are separated from just okay sleeping bags. Although I didn’t get any temps that pushed the lower limit of this bag while testing it out (-20 comfort and -40 lower limit), I can tell you what I did find: These bags are WARM. In fact, during my testing, I needed to keep this bag unzipped until the temps dropped below about 5 degrees so I didn’t overheat. At 10 degrees, I was getting too warm with it zipped all the way up, so I opened it up until later in the night when temps dropped a bit.

Sea to Summit Alpine Sleeping Bag Review

Once it dropped below zero, I zipped it up all the way and remained absolutely toasty warm all night long. I didn’t need to button it all the way down though (with the draw strings around the head and face), so this bag had a long ways to go before I would have gotten cold. In my experience testing many other bags, when you need to cinch down the draw strings, you are starting to get close to that lower comfort range of the bag. I didn’t even come close to that here with the Alpine bag at -1 degrees. I was still on the warm side even at -1.

Sea to Summit Alpine Sleeping Bag Review

I even had clumps of ice form on the outside of the bag from the condensation of my breath, but I stayed absolutely warm. Judging by the outside of the bag, you would never know how toasty warm I was inside the bag.

Of course, as with any sleep system, you’ll need to make sure you use a good, high R-Value pad appropriate for the temps you will be in. Your pad’s R-Value can be a determining factor in whether or not you stay warm. While testing this Alpine bag, I was using the Sea to Summit Ether Light XT Extreme with an R-Value of 6.2 – plenty warm enough for the conditions I was in.

Versatility: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

One of very unique things I came to love while doing this Sea to Summit Alpine sleeping bag review is how you have an extra 1/4 length zipper on the side opposite the main zipper. This allows you to vent the bag or even unzip it and put your arm out if needed when the temperatures aren’t quite that cold.

Sea to Summit Alpine Sleeping Bag Review

I found this to be very useful and it was very effective giving me just enough ventilation to not have to unzip the main zipper. By buttoning the two buttons that goes over each of the zippers, then unzipping each side just a little, I was able to maximize the temperature range of the bag.

Sea to Summit Alpine Sleeping Bag Review

Using the buttons like this worked extremely well, because I still needed a lot of the warmth that this bag offers (It was 5 degrees after all), but being fully zipped up was too much warmth with this bag. Being able to unzip it but having the buttons keep that top flap still in place was perfect.

Another very useful design feature is the ability to completely unzip both sides of the top 1/4 of the bag. If temperatures are just way too warm for the bag, simply unzip both sides and you can either drape if over you loosely or fold it back entirely. That’s a useful design for those warmer nights given the extreme warmth of this bag.

Sea to Summit Alpine Sleeping Bag Review

Drawstring & Hood: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

The draw strings Sea to Summit uses are extremely well made and very durable. They are thick, almost like a paracord, so you don’t have to worry about breaking them. They utilize a push-button style clasp to make it easy to use the draw cord in the dark and easy to find when you need to loosen it up to get out of the bag.

Sea to Summit Alpine Sleeping Bag Review

The Alpine Sleeping bag also features highly technical draft collars to seal out the frigid air. I can say that, after having tested many, many sleeping bags, the draft collars in the hood of this bag are one of my favorites. When you unzip the bag, you can see how they designed this bag to provide you with a full 360 degrees of draft collar just in the hood. Use the draw cord to cinch that down around your face and you’ll easily prevent cold air from entering your bag.

Sea to Summit Alpine Sleeping Bag Review

On top of that, you’ve got a secondary draft collar that is attached to the top portion of the Alpine bag to provide further protection from the cold. This combination provided the tightest seal of any bag I’ve tested so far. I was very impressed. The hood was the perfect surrounding for my head, and I didn’t find myself battling any cold spots, even at -1 degrees (I didn’t even have a hood or beanie on).

Sea to Summit Alpine Sleeping Bag Review

Down/Materials: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

The Sea to Summit Alpine sleeping bag is built with top tier materials as you’d expect from Sea to Summit. 850+ UTLRA-DRY Goose down that is RDS certified, combined with a Free-Flow YKK zipper and Sea to Summit’s Nano Shell is built to handle extreme weather.

Sea to Summit Alpine Sleeping Bag Review

The Nano Shell is unique in that it is windproof and very water resistant (See picture above with moisture beading up on the bag). Having a water resistant shell is a big deal when in extreme weather, and especially when your insulation is down.

Sea to Summit Alpine Sleeping Bag Review

As you can see above, the Sea to Summit Alpine sleeping bag has an incredible amount of loft. With an insane 44 ounces of premium goose down, the Alpine ApIII is stuffed to the gills with down to keep you comfortable in frigid temperatures.

Footbox: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

The Sea to Summit Alpine Sleeping bag features an oversized footbox designed to give your feet the space needed so your feet don’t push against the down, causing a cold spot.  I found the footbox to be extremely comfortable, providing plenty of warmth. The footbox features horizontal baffles rather than vertical baffles which transitions about mid waist to vertical baffles.  The footbox appears to have some added down as my feet never even hinted at getting cold.

What I Liked: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

There’s really only one reason you bring a bag like the Sea to Summit Alpine into the backcountry: to stay warm in really cold temperatures. That’s what it’s built and designed for. From its highly technical hood to the top shelf materials, to the free flow, no snag zipper to the windproof and water resistant Nano Shell, this is a technical mountaineering sleeping bag. Because of some recent hunts in temperatures pushing towards -20, a Sea to Summit Alpine sleeping bag review has been something I’ve been wanting to put together for some time.

While this year temps didn’t quite get that cold, I’m fully confident that this Alpine bag will perform down to its stated -20 comfort rating based on the testing I did. Here’s what I really liked:

  • Weight (for its warmth)
  • Hood & draft collar design
  • Free-flow, no snag zipper
  • Footbox
  • Nano Shell material
  • Quality
  • Incredible warmth
  • Compression bag & long term storage bag included

What I Didn’t Like: Sea to Summit Alpine Sleeping Bag Review

Sea to Summit Alpine Sleeping Bag Review

There was really only one very small issue I had with the Alpine sleeping bag, and that was that I had one of the push button clasps on the draw string come off when using it. It was easily snapped back into place, but I thought it was odd that it came off.

As you can image, the stuffed size of 14.7L is pretty large, but then again, this is a -40 sleeping bag. What do you expect?

  • Draw string snap came off
  • Large stuffed size

How to Store a Down Sleeping Bag

Sea to Summit Alpine Sleeping Bag Review

I love that Sea to Summit gives you a nice zippered, long-term storage bag as well as a compression stuff sack with the Alpine sleeping bag. The compression stuff sack is critical, especially in getting the size of this bag to a minimum when backpacking with it.

Now, when it comes to long-term storage, it’s easy to get home from your final adventure of the season, unload your gear, and throw it all in a storage bin for the off season, but make sure you properly store your down sleeping bag as well as your insulated sleeping pad. Don’t leave that high quality sleeping bag in its stuff sack long-term as it could reduce the effectiveness of the down. Down needs to be lofted, not compressed when stored, and should be stored indoors if at all possible.

Here are a couple of storage options to keep your down sleeping bag at its peak performance:

  • Hang in a closet
  • Lay under your bed
  • Store in the storage sack provided (shown above)

Hanging a down bag is my first choice, but not everyone has the space for that. Most bags come with sewn in loops to stick on a hanger. Second to that, I prefer to store the bag lying flat under my bed. This allows the down to be fully lofted. Finally, storing it in the provided storage sack is perfectly acceptable as well. The down is slightly compressed in those storage sacks, but nothing that will cause any damage to the down in your bag.

Picking the Right Sleeping Pad

Sea to Summit Alpine Sleeping Bag Review

Selecting the right sleeping pad is even more critical when in cold weather, so make sure you get one that’s warm enough. A good high R-Value pad like this Sea to Summit Ether Light XT Extreme with a 6.2 R-Value will add a few degrees to most sleeping bags and at a minimum, give you the most performance out of whatever sleeping bag you are using.

Using a higher R-Value pad will ensure that you are getting everything possible out of your sleeping bag or quilt. Often times, it’s worth the few extra ounces if temperatures may be pushing towards the lower limit of your sleeping bag or quilt.

Check out our sleeping pad reviews for some great options with a quilt! Not digging a quilt? We’ve tested a ton of sleeping bags as well. Check out our sleeping bag reviews!

My ratings for the Sea to Summit Alpine Sleeping Bag

Value
Weight
Sizing
Quality
Packability
Warmth
Overall Ranking

Conclusion: Sea to Summit Alpine Sleeping Bag Review

So, after doing this Sea to Summit Alpine Sleeping bag review would I recommend the Alpine sleeping bag?  If you are looking for an insanely warm, high quality winter sleeping bag with all the bells and whistles, but is still extremely lightweight (relative to its warmth), then the answer is a resounding YES!

However, unless you need the warmth this Alpine sleeping bag offers, you will find yourself taking up a lot of space in your pack and overheating in this bag. I found the best use of the Alpine bag to be when temperatures were below 10 degrees, but it really shined once temperatures dropped below zero. This thing is a beast of a sleeping bag made for extreme cold weather!

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