Sea to Summit Reactor Thermolite Liner
Boost your sleeping bags warmth with this cosy Thermolite liner from Sea To Summit. The Thermolite Reactor Sea to Summits most popular sleeping bag liner. The minimalist design delivers a lightweight and practical way to add warmth to an existing sleeping bag across a range of pursuits from backpacking to alpine trekking, family camping and more. The cosy Thermolite fabric provides an excellent warmth-to-weight ratio, increasing the performance of your sleeping bag by up to 8c while remaining breathable to wick heat moisture away from the body keeping you dry.The Thermolite Reactor can be used on its own or as a sleeping bag liner to boost insulation in colder weather. Liners also help in keeping your sleeping bag cleaner and fresher for longer by reducing the build-up of dirt and oils. Great for a range of travelling experiences, from alpine and backcountry tours to tropical camping, backpacking and anywhere else you choose to lay your head.The tapered shape takes up little pack space and offers peace of mind that should the nights turn cool or the accommodation falls short of expectations you can curl up in comfort for a good nights sleep. At 248g its small enough to fit in a pocket A drawcord hood helps seal out the cold while contrasting colour along the top edge lets you find the entrance quickly in low light. A boxed foot end lets your feet rest in a more natural position. The Thermolite Reactor from Sea to Summit a travel essential with assured quality and 3-season versatility.
Boost your sleeping bags warmth with this cosy Thermolite liner from Sea To Summit. The Thermolite Reactor Sea to Summits most popular sleeping bag liner. The minimalist design delivers a lightweight and practical way to add warmth to an existing sleeping bag across a range of pursuits from backpacking to alpine trekking, family camping and more. The cosy Thermolite fabric provides an excellent warmth-to-weight ratio, increasing the performance of your sleeping bag by up to 8c while remaining breathable to wick heat moisture away from the body keeping you dry.The Thermolite Reactor can be used on its own or as a sleeping bag liner to boost insulation in colder weather. Liners also help in keeping your sleeping bag cleaner and fresher for longer by reducing the build-up of dirt and oils. Great for a range of travelling experiences, from alpine and backcountry tours to tropical camping, backpacking and anywhere else you choose to lay your head.The tapered shape takes up little pack space and offers peace of mind that should the nights turn cool or the accommodation falls short of expectations you can curl up in comfort for a good nights sleep. At 248g its small enough to fit in a pocket A drawcord hood helps seal out the cold while contrasting colour along the top edge lets you find the entrance quickly in low light. A boxed foot end lets your feet rest in a more natural position. The Thermolite Reactor from Sea to Summit a travel essential with assured quality and 3-season versatility.
Boost your sleeping bags warmth with this cosy Thermolite liner from Sea To Summit. The Thermolite Reactor Sea to Summits most popular sleeping bag liner. The minimalist design delivers a lightweight and practical way to add warmth to an existing sleeping bag across a range of pursuits from backpacking to alpine trekking, family camping and more. The cosy Thermolite fabric provides an excellent warmth-to-weight ratio, increasing the performance of your sleeping bag by up to 8c while remaining breathable to wick heat moisture away from the body keeping you dry.The Thermolite Reactor can be used on its own or as a sleeping bag liner to boost insulation in colder weather. Liners also help in keeping your sleeping bag cleaner and fresher for longer by reducing the build-up of dirt and oils. Great for a range of travelling experiences, from alpine and backcountry tours to tropical camping, backpacking and anywhere else you choose to lay your head.The tapered shape takes up little pack space and offers peace of mind that should the nights turn cool or the accommodation falls short of expectations you can curl up in comfort for a good nights sleep. At 248g its small enough to fit in a pocket A drawcord hood helps seal out the cold while contrasting colour along the top edge lets you find the entrance quickly in low light. A boxed foot end lets your feet rest in a more natural position. The Thermolite Reactor from Sea to Summit a travel essential with assured quality and 3-season versatility.
Boost your sleeping bags warmth with this cosy Thermolite liner from Sea To Summit. The Thermolite Reactor Sea to Summits most popular sleeping bag liner. The minimalist design delivers a lightweight and practical way to add warmth to an existing sleeping bag across a range of pursuits from backpacking to alpine trekking, family camping and more. The cosy Thermolite fabric provides an excellent warmth-to-weight ratio, increasing the performance of your sleeping bag by up to 8c while remaining breathable to wick heat moisture away from the body keeping you dry.The Thermolite Reactor can be used on its own or as a sleeping bag liner to boost insulation in colder weather. Liners also help in keeping your sleeping bag cleaner and fresher for longer by reducing the build-up of dirt and oils. Great for a range of travelling experiences, from alpine and backcountry tours to tropical camping, backpacking and anywhere else you choose to lay your head.The tapered shape takes up little pack space and offers peace of mind that should the nights turn cool or the accommodation falls short of expectations you can curl up in comfort for a good nights sleep. At 248g its small enough to fit in a pocket A drawcord hood helps seal out the cold while contrasting colour along the top edge lets you find the entrance quickly in low light. A boxed foot end lets your feet rest in a more natural position. The Thermolite Reactor from Sea to Summit a travel essential with assured quality and 3-season versatility.
in 7 offers
The lowest price for Sea to Summit Reactor Thermolite Liner right now is $69.90 at Snowys Outdoors, compared across 7 retailers.
The all-time low was $52.99 on 5 July 2025 — today's price is 32% 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 12:08:34
Thermolite Reactor Liner
Free 60-day returns
Reactor Thermolite Liner (adds up to 14°F) | Mummy - Black | Sea To Summit
Sea To Summit - Reactor Thermolite Liner - Regular
Delivery between 18–26 June $10
Sea To Summit Reactor Thermolite Liner
S/B Liner Reactor Thermalite
Sea To Summit Thermolite Reactor Liner
Free delivery
Sea To Summit Thermolite Reactor Multi Thermolite. 210 X 90 Cm From
Free delivery
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originally posted on backcountry.com
Bought this to supplement my 39F-rated REI Magma bag on a recent backpacking trip to Alaska and I'm glad I did. Temps dipped into the low 30's F and it rained a lot overnight resulting in a humid, wet tent interior. Not only did the liner add significant warmth to my bag, but it adds a really cozy feeling. I was able to sleep in just a thin base layer without the need for a hat or super thick socks. It's a little bit awkward to get in and out of (especially in the middle of the night should you need to jettison some fluids), but well worth it. I can see this adding enough warmth to take my 39F bag down to the mid 20's without issue.
originally posted on REI
I got this along with a Nemo Disco 15 for extended backpacking trips in cold weather. The material, while thin, is super soft and lightweight. My partner and I used them in Northern Michigan inside of our sleeping bags (with a 15 degree lower limit) and slept comfortably through the night in 10 degree weather. I've yet to use it on it's own in warmer tempts, but can imagine it will perform just as well.My only thing is it can sometimes be a little awkward getting in and out of, it just seems to me like there is a lot of extra fabric, but that's not really enough to deduct a star or impact what it's supposed to do.
originally posted on REI
I've been looking for a soft and warm sleeping bag liner for some time now and this one is it. I typically get cold when I sleep so I really wanted an extra layer just in case.On a recent trip to Dolly Sods, I paired this with a 40 deg BA Echo Park and a R 4.5 sleeping pad. The night-time temps were expected to be in the 50s and I didn't want to take any chances of having a bad night sleep. I was toasty warm and comfortable the whole night.This liner is soft and not slippery, of which I am a fan. I really don't enjoy the silky slippery feel of a sleeping bag, and this feels much more like a sheet that I am used to.One must enter the liner from the top - there is no side zipper, buttons or fasteners. Because the top opening is large, this isn't a huge problem ... MoreI've been looking for a soft and warm sleeping bag liner for some time now and this one is it. I typically get cold when I sleep so I really wanted an extra layer just in case.On a recent trip to Dolly Sods, I paired this with a 40 deg BA Echo Park and a R 4.5 sleeping pad. The night-time temps were expected to be in the 50s and I didn't want to take any chances of having a bad night sleep. I was toasty warm and comfortable the whole night.This liner is soft and not slippery, of which I am a fan. I really don't enjoy the silky slippery feel of a sleeping bag, and this feels much more like a sheet that I am used to.One must enter the liner from the top - there is no side zipper, buttons or fasteners. Because the top opening is large, this isn't a huge problem for me and I was able to wiggle in for a good night's rest. Getting out was easier.I am 6'3" and this was just the right length for me. I weigh 185 lbs and it was wide enough as well.
| Style | Regular (82x36) |
| Length | 9 inches |
| Shape | Mummy |
| Outer Material | Nylon |
| Sport | Camping & Hiking |
Thermolite Reactor Liner
Free 60-day returns
Reactor Thermolite Liner (adds up to 14°F) | Mummy - Black | Sea To Summit
Sea To Summit - Reactor Thermolite Liner - Regular
Delivery between 18–26 June $10
Sea To Summit Reactor Thermolite Liner
S/B Liner Reactor Thermalite
Bought this to supplement my 39F-rated REI Magma bag on a recent backpacking trip to Alaska and I'm glad I did. Temps dipped into the low 30's F and it rained a lot overnight resulting in a humid, wet tent interior. Not only did the liner add significant warmth to my bag, but it adds a really cozy feeling. I was able to sleep in just a thin base layer without the need for a hat or super thick socks. It's a little bit awkward to get in and out of (especially in the middle of the night should you need to jettison some fluids), but well worth it. I can see this adding enough warmth to take my 39F bag down to the mid 20's without issue.
I got this along with a Nemo Disco 15 for extended backpacking trips in cold weather. The material, while thin, is super soft and lightweight. My partner and I used them in Northern Michigan inside of our sleeping bags (with a 15 degree lower limit) and slept comfortably through the night in 10 degree weather. I've yet to use it on it's own in warmer tempts, but can imagine it will perform just as well.My only thing is it can sometimes be a little awkward getting in and out of, it just seems to me like there is a lot of extra fabric, but that's not really enough to deduct a star or impact what it's supposed to do.
I've been looking for a soft and warm sleeping bag liner for some time now and this one is it. I typically get cold when I sleep so I really wanted an extra layer just in case.On a recent trip to Dolly Sods, I paired this with a 40 deg BA Echo Park and a R 4.5 sleeping pad. The night-time temps were expected to be in the 50s and I didn't want to take any chances of having a bad night sleep. I was toasty warm and comfortable the whole night.This liner is soft and not slippery, of which I am a fan. I really don't enjoy the silky slippery feel of a sleeping bag, and this feels much more like a sheet that I am used to.One must enter the liner from the top - there is no side zipper, buttons or fasteners. Because the top opening is large, this isn't a huge problem ... MoreI've been looking for a soft and warm sleeping bag liner for some time now and this one is it. I typically get cold when I sleep so I really wanted an extra layer just in case.On a recent trip to Dolly Sods, I paired this with a 40 deg BA Echo Park and a R 4.5 sleeping pad. The night-time temps were expected to be in the 50s and I didn't want to take any chances of having a bad night sleep. I was toasty warm and comfortable the whole night.This liner is soft and not slippery, of which I am a fan. I really don't enjoy the silky slippery feel of a sleeping bag, and this feels much more like a sheet that I am used to.One must enter the liner from the top - there is no side zipper, buttons or fasteners. Because the top opening is large, this isn't a huge problem for me and I was able to wiggle in for a good night's rest. Getting out was easier.I am 6'3" and this was just the right length for me. I weigh 185 lbs and it was wide enough as well.
Literally, adding the Reactor liner made NO difference to my cold weather comfort compared to sleeping without it. None. Tested this weekend on consecutive nights, with me using the liner on the slightly colder night. On the colder night I woke up cold and needed to put an extra shirt on. It was extremely awkward to get into. A complete waste of money. I'll be returning it for a refund.
I needed a liner to add a few degrees to my sleep set up for a short thru hike. I ultimately choose this liner for the price point. It added the most warmth while still not weighing a lot more or costing a ton. I love the texture and the soft material it’s made out of. I used it with an Enlightened Equipment 40* quilt and stayed warm and cozy in the mid 30*F. It washed easy and helped keep my Quilt clean. Definitely plan on using it on many more trips.
I bought the bag liner for both a washable insert and to add warm to my summer bag and -6 bag. I expect to use it with the summer bag or on its own to shed the weight of the down bag when it’s not 100% necessary.I found I shed my socks and long johns while sleeping outside in Ontario mid-December so the warmth factor is there. I’d say to be conservative say it adds 4 degrees to your bag rating. It definitely adds a bit of awkwardness getting in and out of bed but that’s a minor inconvenience.
Great on a cool night camping, not a cold night,but just right for me in my companion pro hiker2 Tent. I didn't use a sleeping bag. My main purpose of purchasing this was to go camping without my sleeping bag. I do adventure bike riding and camping and like to keep my pack weight down. I think the reactor will work well in winter in Queensland in a tent when you use thermals when in the reactor... It works for me..
I camp throughout the year in and around Texas. For much of the year, in warm weather, a sleeping bag is not required in this area. I have used this liner multiple times and it is exactly what is needed as a warm weather pull-over for a good nights sleep. It keeps me warm enough in the early morning. Its packs small enough that it has permanent place in my backpack now.
Works well. Light weight and easy to stuff. I paired this with my 40 degree bag and slept alright in 35 degree weather. Would have chosen a warmer bag if anything. Also wore sweatpants, hoodie, and beanie cap. My fleece kept me super warm, but was also heavy and took up a lot of space. I plan on using this on 40-60 degree nights now with my bag.
Very stretchy with thermal threads. You can cross legs so easily. It is warm but the actual temperature you feel depends on your metabolism. Since my metabolism is low, I feel it adds up only 3 to 4 degrees Celsius especially in autumn. If your metabolism is low like me, you may consider Reactor Extreme instead.
| Style | Regular (82x36) |
| Length | 9 inches |
| Shape | Mummy |
| Outer Material | Nylon |
| Sport | Camping & Hiking |
