Open main menu

Sea to Summit Trek TK II

rated 5.0 of 5 stars
photo: Sea to Summit Trek TK II 3-season down sleeping bag

Good blend of performance, weight, and price.


  • Lightweight
  • Warm
  • Semi-rectangular/semi-mummy shape
  • Very good value
  • Opens up fully for use as blanket, or for airing out.


  • Could be lighter
  • Zipper system can be confusing
  • Hood does not have an "in-between"—Either it lies flat, or you have to cinch it up fully

Spent WAY too much time searching for a sleeping bag that hit my top three "must haves"

  • Lightweight
  • Warm
  • Not constricting

Tried Big Agnes, North Face, a very attractive offering from Thermolite, REI's own brand, etc...  Finally decided on the Trek TKII after a test of the TK I version at my local REI.  It met my top three musts closely enough to earn a top rating.

The Good:

This is a semi-rectangular bag, not a mummy bag. That means is the shape is mummy like, but the footbox is much wider than a traditional mummy bag. I am not claustrophobic, but I am also not comfortable enough to sleep when my feet are restricted from movement. This bag allows that without adding the weight and bulk of a rectangular bag.

Speaking of bulk, the bag compresses down excellently (probably because of the S2S compression sack included). Compact to the point it flops around in the sleeping bag compartment of my backpack if I do not pack other items in with it.

The bag keeps you warm. I have used it with a Big Agnes insulated pad everywhere from Death Valley—the Mesquite Springs campground (the coldest I ever felt camping BTW)—to Denali National Park. It has performed well in 28 degree temps and in a mountain pass with high winds. Warm enough that you do not want to get out, no matter how bad you need to wee. You do feel the chill when you approach the bag rating though, but that is normal from any bag.

The bag opens up fully, so it can be used as a blanket, and it makes it much easier to air it out after a few days in the backcountry. The zipper also allows you to open up the foot box independently, a real benefit for me. And, it is a separate independent zipper, not just a two way.

Cleaning is simple as putting it into the included cotton bag, and running it through a cold cycle.

The provided storage bag, stuff sack, and (as noted above) washing bag increase the overall value. The stuff sack is a Sea to Summit compression sack, not some cheapie bag with a drawcord.

The bad:

The hood has, from my experience, two configurations. Lay flat, or fully cinched up. There is no in between where it is cinched up just enough to keep your camp pillow in place, but not enough to overheat your head. 

The bag takes a bit of shaking to get it puffed up from storage. Not an excessive amount of time, but I do pull the bag out, then work on inflating my pad.

Because it is semi-rectangular, the bag is going to be heavier than a minimalist bag.

It does not live up to the temp rating, but that is normal. (When a bag is rated to +15 degrees, you add 10 degrees for comfort.)

The ugly:

Not much really. Most of the ugly happens in a lot of other brands/bags. Few of the highlights are:

  • The zippers tend to grab the bag material, but I have not found a bag that does not do that.
  • The two zippers (main/body one, and foot box specific one) overlap by several inches. In order to open the bag fully, or pack it away, you have to do some finger (and mental) gymnastics. Takes a few tries, but easy when you get it down pat.
  • When used as a blanket, the hood gets in the way, especially if two people are sharing.

Final notes:

Any piece of gear is a tradeoff between any number of factors. This bag did not hit any of my top three must haves at 100%, but it was above 90% for them. Other nice to haves include the storage and washing bag, a StoS compression sack for the trail, the double zippers, etc... Overall a solid piece of gear.


Have owned this bag since 2015, used dozens of times, mainly across Alaska, but in the lower 48 as well. Three- and five-night backpacking trips.
Have tested or tried about a dozen bags before selecting this one.

Source: bought it new
Price Paid: $249 (I think...)

Excellent down bag for a variety of conditions. It's lightweight, packs down small, does better in wet weather than other down bags, and is very comfortable.


  • Packs down small
  • Dries fast for a down bag
  • Roomy and comfortable
  • Good compression sack included
  • Lightweight


  • None

This is the fourth backpacking sleeping bag I've purchased, and the second down bag. I purchased it when backpacking in Chile in 2012, realizing that the very lightweight synthetic bag that I had with me at the time would not keep me warm further south in Patagonia. I used it camping in all conditions in southern Chilean Patagonia, as well as many other places in South America and the U.S., and this bag has proven itself again and again as one of the best pieces of gear that I own.

One of the most notable points about this bag is how small it compacts. Sea to Summit makes excellent compression sacks, and they include a custom compression sack with the bag (as well as a storage sack and a cotton sack to wash the bag in). When fully cinched down, the bag compresses to a ball about 7" in diameter. When I compare this to my other down bag, which was more expensive and supposedly warmer than this Sea to Summit Trek II, the other down bag was about double the size of the Trek II when fully compressed. 

The Trek II does an excellent job in semi-cold weather. I've used this bag in snowy conditions numerous times, though probably not much lower than 20 deg F, and slept warmly. This bag seems to be warmer than other bags that are similarly rated — I'm not sure how they do that, but Sea to Summit's down or design does a better job than my similarly temperature-rated Sierra Designs synthetic bag and my RAB down bag. I've also gotten it a little wet and it was not too bad from a comfort or temperature perspective. In contrast, my RAB bag seems to get wet very easily and loses all of its heat when it does.

The boxy design is very comfortable if you don't like the full mummy-style sleeping bags. The hood cinches down well around your face, and helps a lot in colder conditions. And the tiny pocket near the top is great for keeping small items easily accessible. I keep a pair of small earplugs in there so I have them when I am sleeping next to friends that snore.

Lastly, I'll point out that the Sea to Summit bags have zippers that are compatible with one another for certain designs, if you get one Left zip bag and one Right zip. With this, my wife got the Sea to Summit Trek III, which is a slightly warmer bag than the Trek II, and we can zip the two bags together. The combined body heat with two bags connected adds a lot of warmth.

Thank you Sea to Summit for making an excellent product.

Source: bought it new

Your Review

Where to Buy

Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support Trailspace's independent gear reviews.

You May Like


short regular long
Price Current Retail: $294.99
Historic Range: $148.05-$369.99
Reviewers Paid: $249.00
Weight 2 lb 3 oz / 1000 g 2 lb 4 oz / 1020 g 2 lb 7 oz / 1110 g
Fill weight 1 lb 2 oz / 500 g 1 lb 2 oz / 500 g 1 lb 3 oz / 550 g
EN comfort 30 F / -1 C
EN lower limit 18 F / -8 C
EN extreme -13 F / -25 C
Fill 650-fill duck down
Shape Semi-rectangular
Max user height 5 ft 7 in / 170 cm 6 ft 0 in / 185 cm 6 ft 8 in / 205 cm
Shoulder girth 59 in / 150 cm 60 in / 152 cm 61 in / 156 cm
Hip girth 58 in / 148 cm 59 in / 150 cm 60 in / 152 cm
Foot girth 39 in / 100 cm 40 in / 101 cm 40 in / 102 cm
Product Details from Sea to Summit »

Recently on Trailspace

Big Agnes Fly Creek UL2 Review

Fire Maple Petrel Ultralight Pot Review