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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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    12 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 synched up when it’s really cold.
    • Item #STS0084

    Tech Specs

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

    Tech Specs

    • Reviews
    • Q & A

    What do you think about this product?

    Have questions about this product?

    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

                  Doesn't add 25 degrees

                    I really hate being cold so got this liner to add warmth to my 30 degree bag. If It added 5 degrees warmth I would be surprised. Will be good at keeping the bag clean, and maybe okay on a warm Florida summer night when a bag is just too warm. Otherwise I found this useless for it's stated purpose.
                    It does fit nicely in the bag and doesn't restrict my movement.

                    G'Day, Sheri -

                    As I mentioned in a previous comment on this page, there are a number of factors which make it difficult to give a precise rating to a thermal liner. Chief among these is the fact that different people sleep either 'warmer' or 'colder' - I'm a warm sleeper, and if I'm speaking with a 'cold' sleeper, I'll tailor product recommendations accordingly. In your case, it may be that a '+15°F' rating is more appropriate for this liner.
                    A second factor which makes this process difficult is the imprecise nature of sleeping bag temperature ratings. There is no mandated standard for temperature ratings in the US (although the European EN rating system is becoming more common), and some bags have somewhat unrealistic numbers embroidered on them. Significantly, the EN rating differentiates between thermal performance for a man and a woman *for the same bag* - part of that 'warm or cold sleeper' concept mentioned above.
                    Another factor often overlooked is the insulative properties of the sleeping pad, which becomes more significant below 30°F as the ground freezes (and may therefore be colder than the ambient air temperature). The 'R' value is key here.

                    I'd be happy to provide more details if you'd like to email me directly at


                    Barry Robertson
                    Customer Relations Manager

                    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.