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  • Sea To Summit - Thermolite Reactor Extreme Sleeping Bag Liner - Orange
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  • Sea To Summit - Thermolite Reactor Extreme Sleeping Bag Liner - Orange

Sea To Summit Thermolite Reactor Extreme Sleeping Bag Liner


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    21 Reviews


    Staying warm means staying happy.

    The Sea to Summit Thermolite Reactor Extreme Sleeping Bag Liner is a great way to get an extra season out of your sleeping bag or stay warm in unpredictable weather. Lightweight and highly breathable Thermolite fabric will add up to 25 degrees Fahrenheit to your bag’s temperature rating at a low cost of 399 grams added to your pack. The Reactor Extreme has a mummy shape to mesh with your sleeping bag and a draw cord hood that can be cinched up when it’s really cold.

    • Item #STS0084

    Tech Specs

    Degrees Added
    25 F
    84 x 36 in
    Claimed Weight
    14 oz
    Recommended Use

    Tech Specs

    • Reviews
    • Q & A

    What do you think about this product?

    Have questions about this product?

    Use it all year

    • Familiarity: I've put it through the wringer

    Not only is this a good addition as a winter liner, it also makes a great summer sleeping bag. I live in Arizona and its nice to have a little something for the summer. It packs well and it is very comfortable. It makes a noticeable difference in the winter.

    Comfy and Warm

    • Familiarity: I've used it once or twice and have initial impressions

    First really cold weekend in November. Carried my new Thermolite and a 20 degree bag on a 3 night trip in Shenandoah NP. I am a VERY cold sleeper, and usually need a bag rated 20 degrees below the actual temperature. It got down to 25 degrees two of the three nights, and I slept snug and warm. This liner makes a huge difference in the temperature, provides a nice soft layer against your skin and keeps your bag clean in the bargain. Is significantly warmer than the regular Thermolite.
    The weight is negligible, given the value added. Highly recommend

    Extra Warmth

    • Familiarity: I gave it as a gift but have feedback to share

    Sleeping bag liners are used to provide just a little extra warmth on those chilly nights. This is a great option for that, Sea to Summit makes really great quality product for those who get out into the backcountry. This liner is really lightweight and goes well with any Sea to Summit sleeping bag/pad combo. I definitely recommend it!

    5/5? 10/10.

    • Familiarity: I've used it several times

    As per usual with Sea To Summit stuff, my expectations were exceeded and I am very happy with my purchase. I used this in combination with an ancient sleeping bag that's on its way out, and was very pleased/somewhat surprised that I stayed comfortably warm all night - it seemed like a bit of a gamble to rely on this super thin little bag to keep me warm. And, as an added bonus, it's small/light enough that it wasn't a big deal to bring it into the cave AND back out again on the same weekend (seriously, this is a huge check in the Pro column because hauling camp gear underground is usually A Big Ordeal)!! Bought a second one of these for a friend who was super impressed with it.

    Love it!

    • Familiarity: I've put it through the wringer

    I used this liner extensively last year from GA to mid VA on the AT. I sleep very cold and was using a 30 degree bag (I absolutely should have been using a warmer one). This liner felt like it saved my life on some of the colder nights (temps in the teens once or tiwce). I loved the warmth it added. Did it add 25 degrees? I think that's hard to quantify, but it definitely was warmer and worth its weight and space. In addition, it allows all the grime from your nasty hiker body to get washed away every so often as opposed to sleeping directly in your bag.

    Exceeded expectations

    • Familiarity: I've used it once or twice and have initial impressions

    The material is very thin and light weight—great for backpacking in cooler temps! I was skeptical how warm this thin material could keep me, but my expectations were exceeded! I'm not sure it gave me exactly 25 degrees to my sleeping bag, but it sure did save me in sub freezing temperatures! The only times I did wake up cold were from tossing and turning and getting the liner tangled in my bag. Once i pulled it back up over my shoulders, I could immediately feel the warmth come back! Definitely a keeper. My only complaint is how easily tangled it gets in your sleeping bag with moving around.

    Toasty warm in the high sierras

    • Familiarity: I've put it through the wringer

    Finally got the chance to put this liner to the test backpacking/ camping in the eastern sierras. I have a 30* bag and am perpetually cold and this liner honestly kept me warmer than I have ever been while camping. I used this in around 30* temps and I had to peal off a layer of clothing because it kept me so warm. Honestly a camping game changer when you aren't ready to upgrade to a warmer sleeping bag but still push the limits of cold in your current bag. This liner is pretty light weight and little stuff sack makes it easy enough to bring on a backpacking trip without adding much weight. Even works great by itself for car camping or warmer temps. I for sure recommend this to anyone out there who wants a little more warmth in their camping experience.

    Legitimately works

    • Familiarity: I've used it several times

    This thing makes a big difference in my superlight 45 degree bag, without adding too much additional weight. I feel comfortable in my bag now well below freezing, and the weight of my pack is not altered that much.

    Makes a Difference

      I have a 0 degree sleeping bag and I bought the liner for when I go winter camping. With the liner and bag I was really warm still when I woke up in the morning. The liner makes a huge difference in the bag, I loved using it when I was winter camping. It fits perfectly in my bag and made it very comfortable still, I love it.

      Perfect for cooler camping

      • Familiarity: I've used it several times

      I have a Marmot NanoWave 55 Sleeping Bag: 55 Degree Synthetic and it's great since most of my camping is done on the east coast in the summer but I was going to Sequoia National Park where it can drop to the high 20s at night. This liner was perfect! It was great because when I was going to sleep the temperature was still in the 50/60s but as the night went on I stayed warm! I did wake up with really cold toes so the second night I added an extra pair of socks for some extra warmth.

      Must have

      • Familiarity: I've put it through the wringer

      To all the backpackers must have.
      I always packed on me when I am out on the road or backpacking to places. I use this sleep liner as a sleeping blanket for summertime, and for a sleep cover overnight on an unsanitized bed in a cheap motel bed or hostel. At least that is what I would do not to get itching overnight on holiday travel. Or use it as a base lay inside the sleep bag. It helps keep your expensive sleep bag clean from body oil, odor, and dirty garments.

      Is little bulky pack because is not a compressible material. But good to have one on aboard.
      This liner is thin, breath through easy. Is a good full head cover blanket on a hot tropical weather night.

      - Overall -
      The liner is not water repellent fabric.
      Very thin, easy to wash and quick dry.

      First impression

      • Familiarity: I've used it once or twice and have initial impressions

      It was cold! my bag was not rated for this kind of cold. Slid into my Sea to Summit Reactor Thermolite extreme bag liner. Became much warmer, and in turn slept much better than the other guys hanging in their hammocks!

      It really makes a difference!

      • Familiarity: I've used it several times

      We purchased this for Ashley because she tends to get cold in the early morning while winter camping.

      At first I was very apprehensive that this very thin polyester liner would make much of a difference.

      So we paired this liner up with her down sleeping bag & she was warm & cozy all night. We camped a week before in the same conditions/temperature & there was a noticeable difference!

      Truthfully claiming a 25 degree increase is a little stretched in my opinion we would rate it 15 degree+, witch I would take any day!

      Plus, it has kind of a silky feel... VERY comfortable.

      Great item

        I'm happy to own this Thermolite Reactor sleeping bag liner. It's surprisingly warm, and served me well by itself while sleeping at friends' houses while traveling with just a day-pack. I can't compare the additional warmth it provided while out hammock camping, but it undoubtedly helped.

        It's sewn all the way up the sides, which is warm, but when combined with a mummy bag in a hammock - getting into this liner can be difficult! I found the best way was to pull the liner over your entire body first, before entering sleeping bag. Just sitting up in the hammock with feet dangling, then pulling the liner up like a pair of pants and then all the way up over the shoulders. Finally, rotating into hammock and sliding feet down into the sleeping bag.

        Better than expected, really.

          I didn't expect to really go for the bag-liner idea in general. But I got this liner on sale and now realize that its a great investment.

          On one cold hammock-bivvy night I used this liner and the temp difference from inside the liner to outside the liner (but still in my 30degree bag) was noticeable. So it unquestionably makes a difference! I'd rate it as +15 degrees IMHO.

          Otherwise, the material is very comfortable (mmm silky smooth, lots of stretch), seems durable, I've washed it once and it felted a little but not anything that affects performance.

          The shape is nice, and I like that it has some extra material and isn't completely minimalistic.

          I look forward to using it by itself in my hammock on warm nights.


            I used this in combination with my 30 degree montbell bag in 20ish degree weather. Granted that's only 10 degrees, I stayed toasty the entire night! At one point I even have to put my feet outside of my bag because they were too hot. Even when my feet were outside the bag and still inside the liner, they still stayed warm for at least an hour before I had to put them back.

            If you use this in combination with cold-weather camping techniques, it can add quite a bit of warmth to your bag. I highly recommend.

            Works Well

              I used this sleeping bag liner in a 30 deg. bag in 15 deg. weather. It definitely adds a noticeable amount of warmth but not 25 deg. For the weight and packability I was satisfied with the amount of extra warmth it provided. I just left it inside my sleeping bag when I rolled it up and was still about to fit the whole thing in the stuff sack.

              Good but not great

                On the packaging it says it adds up to 25 degrees to your sleeping bag but i wouldn't recommend it for more then 10 degrees. It is extremely light weight at only 14 oz. It fits well into both my -30 and my 20 degree sleeping bags and doesn't add very much size at all to the stuff sac. I would say its better for summer camping to use on those nights where its chilly but not cold enough for a bag.

                G'Day Sean -

                The Thermolite Reactor Extreme has been tested by a number of individuals using various sleeping bags in a variety of climatic conditions: a gain of *up to* 15°C (25°F) was held to be realistic. However - the key to the above sentence is that it contains a number of variables: each sleeper's metabolism is different, each sleeping bag construction is different [and the temperature 'rating' supplied by the manufacturer may be more or less realistic], and the weather on each test location was different.
                Personally, I'm a warm sleeper, and I'd give a temperature plus of 10°C / 18°C to my *Standard* (ie non-extreme) Thermolite Reactor, but I have friends who sleep much colder for whom a plus of 5°C / 8°F seems more reasonable for 'my' liner.

                Please feel free to contact me at if you'd like more details

                Barry Robertson, Customer Relations Manager

                Like a sheet in your bag

                  I like this liner although its not a 25deg increase to your bag's rating, feels more like 10-15. It has a nice feel & is comfortable alone on hot summer nights or in combo w 40deg bag. Price is a bit steep @ $65

                  Unanswered Question

                  Would this liner and my Marmot trestle 0 be sufficient for Aconcagua? The packing list sugest a -25 down/synthetic bag by itself - but I'm wondering if this liner will really add 25° of added warmth, and a combination of this liner, trestle 0 & my Northface Himalayan Park will be enough at night as I know Aconcagua can be brutal.

                  Unanswered Question

                  What are the dimensions of this when packed up in stuff bag?

                  I am hiking in mid-northern Spain (on the...

                  I am hiking in mid-northern Spain (on the Camino near Santiago) in early June. I do not want to take a sleeping bag and a liner. Is this Thermolite bag liner good enough to take by itself. Does it have a zipper all around it? (Thinking about bed bugs, too. )



                  Best Answer


                  In terms of knowing if this will be warm enough as a stand alone product for you, really only you'd be able to know through some trial and error. Some things to keep in mind:

                  -Night time temperatures in Spain?

                  -How does your body regulate heat while sleeping?

                  -What other layers will you be wearing to bed?

                  -Are you hammocking or sleeping on the ground?

                  -Are you in a shelter?

                  If you are hot blooded and the nights are warm and you're on the ground, then this could work great. But if one of those three things is a no for you, then I'd be incredibly hesitant and recommend trying it out before your trip.

                  At the top of the liner their is a draw cord for synching it tight around the head. The zipper is a left handed zipper that runs from the shoulder to mid shin.

                  Hope this helps!

                  Jared D.


                  800.409.4502 ext 4055

                  On the Camino, you will probably be sleeping indoors, albeit not always with heating systems. A room full of bodies can get pretty warm. This product should suffice in June. You will probably want to take a light base layer -- long bottoms and top -- to wear either day or night if you are the cold type (I am!). Something like Patagonia Silk weight or Icebreaker 150 (my preference). Note: you will probably want to sleep in at least boxers and a tank as you don't have much privacy in the pilgrims' lodgings. It will most likely range from pleasant to unbearably hot most days and nights. However, it can get quite cool.

                  I have a Western Mountaineering 35 degree...

                  I have a Western Mountaineering 35 degree bag. Would you trust this liner with that bag climbing Baker and Rainier in the early summer and camping in the cascades in early spring?


                  Matai, I don't think it would be warm enough for most people as they seem to go for at least a 10 degree bag. Of course everyone is different, add a good pad and sleep in your down and you might be ok but I wouldn't want to chance it. I don't believe the 25 degree rating they claim but that is only my opinion.