Sea to Summit Reactor Extreme Thermolite Liner
Increases sleeping bag performance by up to 14 C (25 F) with super-insulating 110g/m Thermolite fabric. Spacious design allows for a comfortable night s sleep, even when the mercury plummets. Thermolite is a hollow core fibre that provides extraordinary warmth for its weight and remains extremely breathable. Adds warmth to a sleeping bag or, used alone, is the ideal warm weather bag. With the stretchy knit fabric that moves with you and a drawcord hood, the Thermolite Reactor Extreme liner is perfect for wrigglers and rollers or anyone who needs some extra warmth. Tapered design from the foot to the head end to reduce weight and increase thermal efficiency. Mummy shaped with boxfoot design for superiro comfort.
Increases sleeping bag performance by up to 14 C (25 F) with super-insulating 110g/m Thermolite fabric. Spacious design allows for a comfortable night s sleep, even when the mercury plummets. Thermolite is a hollow core fibre that provides extraordinary warmth for its weight and remains extremely breathable. Adds warmth to a sleeping bag or, used alone, is the ideal warm weather bag. With the stretchy knit fabric that moves with you and a drawcord hood, the Thermolite Reactor Extreme liner is perfect for wrigglers and rollers or anyone who needs some extra warmth. Tapered design from the foot to the head end to reduce weight and increase thermal efficiency. Mummy shaped with boxfoot design for superiro comfort.
Increases sleeping bag performance by up to 14 C (25 F) with super-insulating 110g/m Thermolite fabric. Spacious design allows for a comfortable night s sleep, even when the mercury plummets. Thermolite is a hollow core fibre that provides extraordinary warmth for its weight and remains extremely breathable. Adds warmth to a sleeping bag or, used alone, is the ideal warm weather bag. With the stretchy knit fabric that moves with you and a drawcord hood, the Thermolite Reactor Extreme liner is perfect for wrigglers and rollers or anyone who needs some extra warmth. Tapered design from the foot to the head end to reduce weight and increase thermal efficiency. Mummy shaped with boxfoot design for superiro comfort.
Increases sleeping bag performance by up to 14 C (25 F) with super-insulating 110g/m Thermolite fabric. Spacious design allows for a comfortable night s sleep, even when the mercury plummets. Thermolite is a hollow core fibre that provides extraordinary warmth for its weight and remains extremely breathable. Adds warmth to a sleeping bag or, used alone, is the ideal warm weather bag. With the stretchy knit fabric that moves with you and a drawcord hood, the Thermolite Reactor Extreme liner is perfect for wrigglers and rollers or anyone who needs some extra warmth. Tapered design from the foot to the head end to reduce weight and increase thermal efficiency. Mummy shaped with boxfoot design for superiro comfort.
in 3 offers
The lowest price for Sea to Summit Reactor Extreme Thermolite Liner right now is $111.99 at Your Outdoor Store, compared across 3 retailers.
The all-time low was $72.88 on 9 Oct 2025 — today's price is 54% above the lowest ever. It has been notably cheaper before — worth setting a price alert.
Prices last updated 14 June 2026.
Last updated at 14/06/2026 12:08:57
Sea To Summit Reactor Thermolite Extreme Liner
Free delivery
Sleeping Bag Liner Reactor Extreme Regular Thermolite Mummy - Sea To Summit - Down South Camping & Outdoors
Sea to Summit Thermolite Reactor Extreme Sleeping Bag Liner - Red, 90 x 210 Centimeter
Delivery between 19–23 June $15.87
originally posted on snowys.com.au
I went camping around Mt. Alexander (central Victoria) in early spring, temps would not have hit 0c but likely floated around 5c or so. In combination with a S2S Th2 5c bag I was surprisingly chilly in the early morning when it was coldest, certainly not comfortable but not freezing. I would be interested to know how/under what conditions S2S determine their stated +15c temperature improvement as I did not receive such an improvement.That said, it took some of the cool edge off, is roomy, is nice to the touch, packs small and is light. You're likely to gain more with a set of mid-tier top and bottom thermals than from this expensive liner, As such I can't really say this liner is good value even when discounted to $80.I can imagine it being a good summer bag ... MoreI went camping around Mt. Alexander (central Victoria) in early spring, temps would not have hit 0c but likely floated around 5c or so. In combination with a S2S Th2 5c bag I was surprisingly chilly in the early morning when it was coldest, certainly not comfortable but not freezing. I would be interested to know how/under what conditions S2S determine their stated +15c temperature improvement as I did not receive such an improvement.That said, it took some of the cool edge off, is roomy, is nice to the touch, packs small and is light. You're likely to gain more with a set of mid-tier top and bottom thermals than from this expensive liner, As such I can't really say this liner is good value even when discounted to $80.I can imagine it being a good summer bag though!DO NOT take this out expecting it to turn your 3 season bag into a 4 season bag or even a 2 season bag into a early spring/later autumn bag, this may be obvious to the experienced campers but it's important to hold companies' marketing to account and this item is advertised as adding 15C to the comfort of your sleeping bag. If you've got the money, then it may be good insurance you can throw in the boot of your car or small pocket of your pack in case the temp dips a touch lower than you planned.
originally posted on seatosummitusa.com
I bought mine on sale and am happy with the purchase. I've used this liner for a couple of years now for occasional spring, summer and fall camping/cottage living. I view it as a functional, warmer version of a typical sleeping bag liner. In very warm weather, I can use it as a standalone cover (sort of like being in bed with just a sheet over you). But it does not give 15 degrees C of extra warmth to the sleeping bag as the weather gets colder. For instance, I cannot imagine it turning a 10 degree C bag into a -5 degree bag. The regular price seems a bit high for what you get, especially considering that it is made in China. I have not used it for backpacking where weight is more of a concern.
originally posted on REI
Seems to work pretty well. I don't know for certain if it really added warmth in subfreezing conditions (used on a three-day, 60 mile trip where temperatures dipped below 30°F at roughly 5,500 feet) but I will say, combined with a 20°F down quilt, I stayed toasty warm and had some remarkable sleep.Night 1 I used it and the wind was howling. I had the vents opened on my tent but the vestibules closed. I was next to a creek and there was a bunch of snow on the ground (but not snowing) and not much protection around me to deflect wind this night. This night I was all bundled up, wearing a puffy jacket, beanie and mid-layer. However, I wasn't wearing socks and I did not experience cold feet.Night 2 I used it and I stayed at a camp spot in the dense forest and it ... MoreSeems to work pretty well. I don't know for certain if it really added warmth in subfreezing conditions (used on a three-day, 60 mile trip where temperatures dipped below 30°F at roughly 5,500 feet) but I will say, combined with a 20°F down quilt, I stayed toasty warm and had some remarkable sleep.Night 1 I used it and the wind was howling. I had the vents opened on my tent but the vestibules closed. I was next to a creek and there was a bunch of snow on the ground (but not snowing) and not much protection around me to deflect wind this night. This night I was all bundled up, wearing a puffy jacket, beanie and mid-layer. However, I wasn't wearing socks and I did not experience cold feet.Night 2 I used it and I stayed at a camp spot in the dense forest and it wasn't as cold as the previous night (though still pretty cold, probably mid-30°Fs). I was only wearing my tights and my compression long-sleeved base layer, as I got way too warm with the puffy jacket on. Also removed my beanie and socks because I got too warm. Slept like a baby. As a matter of fact, I slept in until 10:00am the next morning (which is way out of the norm for me, normally I'm up at 6:00am when backcountry hiking).All in all, I am convinced it made me warmer, but to what degree (no pun intended)? Not exactly sure as it's hard to give an answer, but what stood out to me was how comfortable it was to use. It felt great on my skin and made it feel like I was in a proper bed as opposed to that sticky, plasticky feel of my down quilt.Summary:PROS:- Very comfortable on the skin- I am convinced it did make my sleep system a bit warmer, particularly on my feet- Easy to wash, and just the fact that it is machine-washable is a great featureOTHER CONSIDERATIONS:- Heavy. There are lower-weight options on the market, but less weight could mean less warmth.- Does not pack down small. Again, this is a winter sleeping accessory so I don't necessarily consider this a bad thing, but just something to consider.- Very long. Knew this getting it, but it's far too long for me and I don't find the hood on it to be very useful. I'll probably have the hood removed and the entire liner cut to my height to make it pack down smaller/weigh less.Overall, for colder conditions, would strongly recommend.
| Style | Extreme (83 X 35) |
| Length | 83 inches |
| Shape | Mummy |
| Outer Material | Nylon |
| Season | Evergreen |
Sea To Summit Reactor Thermolite Extreme Liner
Free delivery
Sleeping Bag Liner Reactor Extreme Regular Thermolite Mummy - Sea To Summit - Down South Camping & Outdoors
Sea to Summit Thermolite Reactor Extreme Sleeping Bag Liner - Red, 90 x 210 Centimeter
Delivery between 19–23 June $15.87
I went camping around Mt. Alexander (central Victoria) in early spring, temps would not have hit 0c but likely floated around 5c or so. In combination with a S2S Th2 5c bag I was surprisingly chilly in the early morning when it was coldest, certainly not comfortable but not freezing. I would be interested to know how/under what conditions S2S determine their stated +15c temperature improvement as I did not receive such an improvement.That said, it took some of the cool edge off, is roomy, is nice to the touch, packs small and is light. You're likely to gain more with a set of mid-tier top and bottom thermals than from this expensive liner, As such I can't really say this liner is good value even when discounted to $80.I can imagine it being a good summer bag ... MoreI went camping around Mt. Alexander (central Victoria) in early spring, temps would not have hit 0c but likely floated around 5c or so. In combination with a S2S Th2 5c bag I was surprisingly chilly in the early morning when it was coldest, certainly not comfortable but not freezing. I would be interested to know how/under what conditions S2S determine their stated +15c temperature improvement as I did not receive such an improvement.That said, it took some of the cool edge off, is roomy, is nice to the touch, packs small and is light. You're likely to gain more with a set of mid-tier top and bottom thermals than from this expensive liner, As such I can't really say this liner is good value even when discounted to $80.I can imagine it being a good summer bag though!DO NOT take this out expecting it to turn your 3 season bag into a 4 season bag or even a 2 season bag into a early spring/later autumn bag, this may be obvious to the experienced campers but it's important to hold companies' marketing to account and this item is advertised as adding 15C to the comfort of your sleeping bag. If you've got the money, then it may be good insurance you can throw in the boot of your car or small pocket of your pack in case the temp dips a touch lower than you planned.
I bought mine on sale and am happy with the purchase. I've used this liner for a couple of years now for occasional spring, summer and fall camping/cottage living. I view it as a functional, warmer version of a typical sleeping bag liner. In very warm weather, I can use it as a standalone cover (sort of like being in bed with just a sheet over you). But it does not give 15 degrees C of extra warmth to the sleeping bag as the weather gets colder. For instance, I cannot imagine it turning a 10 degree C bag into a -5 degree bag. The regular price seems a bit high for what you get, especially considering that it is made in China. I have not used it for backpacking where weight is more of a concern.
Seems to work pretty well. I don't know for certain if it really added warmth in subfreezing conditions (used on a three-day, 60 mile trip where temperatures dipped below 30°F at roughly 5,500 feet) but I will say, combined with a 20°F down quilt, I stayed toasty warm and had some remarkable sleep.Night 1 I used it and the wind was howling. I had the vents opened on my tent but the vestibules closed. I was next to a creek and there was a bunch of snow on the ground (but not snowing) and not much protection around me to deflect wind this night. This night I was all bundled up, wearing a puffy jacket, beanie and mid-layer. However, I wasn't wearing socks and I did not experience cold feet.Night 2 I used it and I stayed at a camp spot in the dense forest and it ... MoreSeems to work pretty well. I don't know for certain if it really added warmth in subfreezing conditions (used on a three-day, 60 mile trip where temperatures dipped below 30°F at roughly 5,500 feet) but I will say, combined with a 20°F down quilt, I stayed toasty warm and had some remarkable sleep.Night 1 I used it and the wind was howling. I had the vents opened on my tent but the vestibules closed. I was next to a creek and there was a bunch of snow on the ground (but not snowing) and not much protection around me to deflect wind this night. This night I was all bundled up, wearing a puffy jacket, beanie and mid-layer. However, I wasn't wearing socks and I did not experience cold feet.Night 2 I used it and I stayed at a camp spot in the dense forest and it wasn't as cold as the previous night (though still pretty cold, probably mid-30°Fs). I was only wearing my tights and my compression long-sleeved base layer, as I got way too warm with the puffy jacket on. Also removed my beanie and socks because I got too warm. Slept like a baby. As a matter of fact, I slept in until 10:00am the next morning (which is way out of the norm for me, normally I'm up at 6:00am when backcountry hiking).All in all, I am convinced it made me warmer, but to what degree (no pun intended)? Not exactly sure as it's hard to give an answer, but what stood out to me was how comfortable it was to use. It felt great on my skin and made it feel like I was in a proper bed as opposed to that sticky, plasticky feel of my down quilt.Summary:PROS:- Very comfortable on the skin- I am convinced it did make my sleep system a bit warmer, particularly on my feet- Easy to wash, and just the fact that it is machine-washable is a great featureOTHER CONSIDERATIONS:- Heavy. There are lower-weight options on the market, but less weight could mean less warmth.- Does not pack down small. Again, this is a winter sleeping accessory so I don't necessarily consider this a bad thing, but just something to consider.- Very long. Knew this getting it, but it's far too long for me and I don't find the hood on it to be very useful. I'll probably have the hood removed and the entire liner cut to my height to make it pack down smaller/weigh less.Overall, for colder conditions, would strongly recommend.
We used this to provide a little extra warmth (in addition to a quilt) on a backpacking trip. The nights were in the low 40s, and typically at that temps the quilt alone doesn't keep me warm enough. These sleeping bag liners really seemed to help keep us warmer, and I actually got a little too warm one night.Length wise the compact version was fine for me (at 5'2"), but my taller husband also opted to use the compact version just to carry less weight. It was a little short on him but worked fine, we're both happy with the purchase.I also liked that these helped keep our quilt cleaner, and then I was able to machine wash these after our backpacking trip. Great purchase!
Purchased because my Sierra 30/40 bag was feeling cold on a fall trip in Northern New Mexico. Noticed an immediate and pleasant difference. Used for 9 additional nights on my October trip through NM, CO, WY, ND, and slept warm. I like how it helps keep the sleeping bag clean, and also how I can put the hood either over my head (standard position) or over my face (reverse position) for additional warmth. The fabric is comfortable, and does not seem to snag on the clothes I wear to bed. I do not mind the lack of a zipper -- it is easy to get into and out of, even confined in a tent. At 6 ft 1 in, the liner is of adequate length. Have washed it three times so far, no problems.
We ordered 3 of these for a 3 day, 2 night backpacking trip in high elevation mountains in Nevada. We just got back from our trip yesterday and are SO glad we ordered these before we left.It was myself, my husband, and our almost 6yr old. It was my & our kiddo's first overnight backpacking trip (husband is a pro). It dropped below freezing both nights we were there.We layered ourselves up (the way you should when its cold out!), then slid into these, then slid into our bags . All our bags were rated at 30* or colder. We all had ThermaRest inflatable sleeping pads to sleep on. We slept in a cozy 3person Kuiu 4 season backpacking tent.These feel like a thinner Jersey Knit material and I honestly was feeling a little skeptical at them adding enough warmth for us to ... MoreWe ordered 3 of these for a 3 day, 2 night backpacking trip in high elevation mountains in Nevada. We just got back from our trip yesterday and are SO glad we ordered these before we left.It was myself, my husband, and our almost 6yr old. It was my & our kiddo's first overnight backpacking trip (husband is a pro). It dropped below freezing both nights we were there.We layered ourselves up (the way you should when its cold out!), then slid into these, then slid into our bags . All our bags were rated at 30* or colder. We all had ThermaRest inflatable sleeping pads to sleep on. We slept in a cozy 3person Kuiu 4 season backpacking tent.These feel like a thinner Jersey Knit material and I honestly was feeling a little skeptical at them adding enough warmth for us to be comfortable. However, the husband was so warm that he ended up sleeping in his underwear and a hoodie! Myself and my kiddo stayed layered up, but were super cozy. I never felt cold. I have no idea the number of "degrees" actually added, but I don't care. It made a difference! The length was way overkill for me and the kiddo - but excess length ended up in the bottom of our bags and didn't cause any discomfort. (They should make these in "short" lengths too! It would cut down on our packing weight).Highly recommend. Worth the added pack weight - sleeping cold is miserable, and the mountains we hiked into unfortunately are known for people getting hypothermia and sometimes dying because of the cold nights! Grateful for these liners.PS- Backcountry Customer Service is AMAZING. I called in because we accidentally picked the wrong shipping option, and they'd be delivered while we were gone on our backpacking trip! They helped us find a solution, and got another round sent out and overnighted them to us. We got them 36 hours in advance and were able to take them Hallelujah.
I was pretty excited to purchase this product as I had expected to use it as a light weight sleep system option. I ended up testing it in the field mid-April in New England. I paired the S2S reactor liner with a hammock, hammock liner, and Army poncho liner during about 35 degree weather. Had my calculations been correct with the layering I should have been amply warm to sleep that night. Unfortunately I spent a solid majority of the night shivering with intermittent moments of sleep, ultimately I am not completely sold on the reactor liner giving an extra 20 degrees to my set up.On the plus side it packs down remarkable small. I will continue to pair this with other sleeping systems to find its perfect operating range.
Seeing a negative review below I think some folks tend to not realize how sleep systems work. Adding this liner to a bag is not going to instantly add 25 degrees. If you are in a situation to warm up your bag you also have to consider factors like a good insulated sleeping pad. Also, most bags are generally rated for their limit, not their comfort level, so you'll need to consider that as well. If you add a good insulated pad, plan around temperature of comfort rating on the bag, and add this liner will give you so much versatility through various seasons.I use this to add to a bag so I don't need to have a second bag. If you add to a 30F, you can drop down well below freezing. If you add to a 15F you can take it from 3-season camping to winter camping (if you add ... MoreSeeing a negative review below I think some folks tend to not realize how sleep systems work. Adding this liner to a bag is not going to instantly add 25 degrees. If you are in a situation to warm up your bag you also have to consider factors like a good insulated sleeping pad. Also, most bags are generally rated for their limit, not their comfort level, so you'll need to consider that as well. If you add a good insulated pad, plan around temperature of comfort rating on the bag, and add this liner will give you so much versatility through various seasons.I use this to add to a bag so I don't need to have a second bag. If you add to a 30F, you can drop down well below freezing. If you add to a 15F you can take it from 3-season camping to winter camping (if you add the insulated pad). Makes you have to carry less or own less.My girlfriend who is always cold uses hers always to add more to her 15 degree bag and it keeps her comfortable through cold temps. It's a boost, it is not exact. I also use it for my 15 bag when winter camping. It adds more comfort and warmth, it is not going to boost 25 randomly. The whole system needs to be considered.The liner is super packable and I will always throw into my bag. It is comfy and I've even used as a pillow. Whenever things get to the cold side I can count on it to warm me up. I like the orange, it is easy to wash as well! So sweaty nights you are not stinking up your down bag and having to google how to wash it. Just wash the liner!Also - in summers or car camping, I will just use the liner as a sleeping bag as itself. It is warm enough for a chilly summer night and is better than a blanket.I'm 6'0, 175 and its plenty of room.
I've used this on a couple dozen nights over a year now. It is very thin and comfy, definitely a bit warmer but not +15C.It is great to add a little bit of warmth, a lot of comfort and can also be used as a light layer during warmer seasons.I had issues with getting clammy during my sleep, as a result any cool light breeze at night would give me great chills and wake me up. This was the solution for me, gets rid of that sticky feel without overheating.Recently went on a 2C night trip and had this over my face too, it was fantastic. Breathable and my nose no longer felt like it was falling off.Also keeps your sleeping bag cleaner for longer :)I highly recommend this product to anyone needing an extra layer (or a single light layer) for their sleep solution
Very useful in adding warmth to a sleeping bag. Noticed a significant difference using this liner. The night before I purchased, my 30/40 Sierra sleeping bag just wasn't enough for the cold NM nights. The night after, I was comfortably warm. Also very useful for keeping sleeping bag cleaner and fresher. Easy to wash. I am 6'1" and find this size is adequate for me. I don't mind the lack of zipper -- it is easy for me to enter and exit as is, and I am somewhat inflexible. Also, as noted in another review, you can flip it around so the longer back is up over your face, providing warmth while still allowing you to breathe easily. The texture of the fabric is pleasant to my bare skin, and has not snagged on any clothing I wear to bed.
| Style | Extreme (83 X 35) |
| Length | 83 inches |
| Shape | Mummy |
| Outer Material | Nylon |
| Season | Evergreen |
