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
What do you think about this product?
February 2, 2020
Toasty....like flannel shhets in your ba
I bought this for a winter campout to use in conjunction with my 30° bag. We slept outside in 22° weather and I never had an issue with being chilly all night. Great extra for those chilly shoulder season nights, mild winter camping and as your only bag for hot summer nights in the hammock. I would definitely recommend this product!
November 21, 2019
Added Comfort for Cold Nights!
I have a 20 degree bag that I use pretty much year round, including summers. So as you can imagine, camping in the winter can be VERY cold for me. This bag liner changes the game! Adding up to 25 degrees to the temperature rating of the bag, I essentially can convert my bag to a 0 degree bag. I used this when I went backpacking in the Sawtooths in Idaho in mid-September when the temperatures at night were sometimes 20 or below. The trip was snowy and wet, so it was a sigh of relief to have this liner to climb into and warm me up at night. It’s mummy shaped so it fit perfectly with my mummy sleeping bag and at 5’2”, it was roomy (length-wise) but still kept me warm. My favorite feature of the liner is the drawcord hood, which retained heat on colder nights. I would suggest this liner to anyone who is looking to get extra use of their current bag that might not be as warm as they are needing!
April 21, 2019
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.
March 21, 2019
Worth the weight and cost
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.
November 1, 2018
Soft, Warm and Heavy for UL Backpacking
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.
November 1, 2018
Hey Katie! Thanks for the review! Glad you're loving the liner so far and can't wait to hear what other adventures you take it on.
October 26, 2018
I love how comfortable it is. I cant believe i went all this time without a liner in my sleeping bag.
October 19, 2018
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.
October 11, 2018
I would have froze without this!
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.
John Peter Barrand
June 5, 2018
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.
May 8, 2018
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.
April 13, 2018
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.
April 4, 2018
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.
January 6, 2018
Use it all year
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.
January 8, 2018
Thanks for the review!
December 10, 2017
Comfy and Warm
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
October 30, 2017
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!
October 25, 2017
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.
October 11, 2017
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.
September 25, 2017
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.
July 22, 2017
It definitely made a difference, maybe not 25 degrees, but it made some cold nights much more bearable!
June 11, 2017
Toasty warm in the high sierras
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.
November 22, 2018
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?
November 24, 2018
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.
November 29, 2017
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. Thanks.
April 23, 2017
What are the dimensions of this when packed up in stuff bag?
January 4, 2014
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. ) Thanks Lita
January 5, 2014
Lita, 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. Gearhead 800.409.4502 ext 4055
May 8, 2014
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.
December 4, 2014
Hi Lita, I will be hiking the Camino in Spain next June. Did you go with this liner? If so, was it enough! Thanks! Hope you had a great experience on the Camino
February 26, 2012
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? Thanks
February 26, 2012
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.