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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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    31 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.

    • Sleeping bag liner adds up to 25 degrees to sleeping bags
    • Thermolite insulation is light, breathable, and packable
    • Included stuff sack
    • 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?

    Extra Warmth

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

    The reviews made me buy it. I'll be living in a tent in Alaska this summer so I'm excited to give this a try to protect my sleeping bag and for the extra warmth.

    Worth the weight and cost

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

    Im new to backpacking and wanted to test run some new gear on a car camp trip before being stuck miles out in a bad situation. Bishop, CA in Feb with temps down to 17°f seemed like a good test.. So my gear to test: Kelty Horizon 2 tent, Nemo Cosmo sleep pad, OutdoorVitals Storm loft 30° syn mummy pod, Sea to Summit Reactor Xtreme liner. Sleeping in my base layer and smartwool socks the first night with my morning clothes tucked in my bag as well, I was not cold. Not warm either just comfortable enough to sleep well. Considering I used the same bag without the liner in 27° prior and was a long cold night, proved the liner was helping. So the second night I added a hot nalgene bottle to my footbox (inside the liner) and was toasty as could be throughout the night. Does the liner add 25°? No it doesn't, but does add considerable warmth to your bag when used properly. The drawstring around the opening is key. Left loose it's pretty much just another bag liner but cinched either around your chest or neck to trap your body heat it really does make a noticeable difference. I wouldn't rely on this setup as a dedicated winter sleep system but having this liner would expand your temperature comfort range in unpredictable weather. Worth the weight in my opinion.

    Soft, Warm and Heavy for UL Backpacking

    • Familiarity: I've used it several times

    The fabric is so soft! Despite being heavier than I'd like, I really enjoyed this liner. I plan to use it for very warm weather backpacking trips instead of a sleeping bag, but haven't done that yet. So far, I've used in conjunction with my 30 degreee Montbell sleeping bag during cold nights. It definitely doesn't add a full 25 degrees from my experience, more like 15.

    A Travel & Camping Essential

      These proved essential on a recent trip to Iceland. We didn't have room for full sleeping bags in our luggage, so we took these to supplement whatever the camper van rental company supplied us with, and I'm very glad we did! These will definitely become a staple in our camping gear.

      I would have froze without this!

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

      I took this to hike Mount Kilimanjaro in Africa and would have froze without it. It's light, but warm. Easy to repack in it's bag and super comfortable. I would take this on every campout for the extra heat.


      • Familiarity: I've used it several times

      This sleeping bag liner is amazing! It’s thin so it doesn’t feel bulky in the sleeping bag but super warm. My 30-degree bag just got a lot better for late season camping. I also really like that it rolls up and fits into such a small, lightweight bag. It doesn’t add much bulk to a pack or bike.

      good liner

      • Familiarity: I've used it several times

      This liner is a great way to add some warmth to any bag. It also helps to keep your bag clean as it acts like a barrier between you and your bag, and is much easier to clean. An added bonus is that the liner can be used as a stand alone sleeping bag during the hot summer months in desert climates.

      Review:sea2summit Reactor extreme liner

        Bought this item for the -20 C nights in a 4 season tent to go inside my sleeping bag, a mountain hardwear 0F bag which is less than hot and lovely when it is below -20C outside. This liner has been great at making up the few degrees needed. Backstory is cold camping in Northern Ontario with snow, Jan-March. Sorry for lack of photos.

        Nice Liner

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

        I gave one of these to my cousin and he's loving the added warmth this brings to his sleeping bag. It's helped him have one sleeping bag that now works across a broader temp range.

        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.

          I know this is a liner typically put inside your sleeping bag. Just curious if it works at all if put on the outside of a down sleeping bag?

          It would help a little bit on the outside, but not to much. I would definitely recommend putting this in the inside of your sleeping and it would keep you a lot warmer. How sleeping bags work also is keeping that condensation on the outside of your bag with the material that the bag uses.

          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.