Add warmth to your sleeping bag with the Sea to Summit Thermolite Reactor Fleece liner, the warmest sleeping bag liner in their Thermolite Reactor range! This compact and lightweight sleeping bag liner can be used to keep the inside your sleeping bag clean as well as to add additional warmth to your sleeping bag in cooler conditions. The Thermolite fleece liner can also be used as a stand alone summer sleeping bag, making it a versatile option for outdoor adventures and travelling abroad. The fleece liner comes in a mummy shape and is made from Thermolite material, which traps air inside the fibres of the liner to provide exceptional warmth. The liner weighs just 379g and packs into a compact ultra-sil stuff sack, with a pack size of 19 x 13cm. Equipped with a panelled draw cord hood for added warmth when required and a quarter zip for ease of use.
Add warmth to your sleeping bag with the Sea to Summit Thermolite Reactor Fleece liner, the warmest sleeping bag liner in their Thermolite Reactor range! This compact and lightweight sleeping bag liner can be used to keep the inside your sleeping bag clean as well as to add additional warmth to your sleeping bag in cooler conditions. The Thermolite fleece liner can also be used as a stand alone summer sleeping bag, making it a versatile option for outdoor adventures and travelling abroad. The fleece liner comes in a mummy shape and is made from Thermolite material, which traps air inside the fibres of the liner to provide exceptional warmth. The liner weighs just 379g and packs into a compact ultra-sil stuff sack, with a pack size of 19 x 13cm. Equipped with a panelled draw cord hood for added warmth when required and a quarter zip for ease of use.
Add warmth to your sleeping bag with the Sea to Summit Thermolite Reactor Fleece liner, the warmest sleeping bag liner in their Thermolite Reactor range! This compact and lightweight sleeping bag liner can be used to keep the inside your sleeping bag clean as well as to add additional warmth to your sleeping bag in cooler conditions. The Thermolite fleece liner can also be used as a stand alone summer sleeping bag, making it a versatile option for outdoor adventures and travelling abroad. The fleece liner comes in a mummy shape and is made from Thermolite material, which traps air inside the fibres of the liner to provide exceptional warmth. The liner weighs just 379g and packs into a compact ultra-sil stuff sack, with a pack size of 19 x 13cm. Equipped with a panelled draw cord hood for added warmth when required and a quarter zip for ease of use.
Add warmth to your sleeping bag with the Sea to Summit Thermolite Reactor Fleece liner, the warmest sleeping bag liner in their Thermolite Reactor range! This compact and lightweight sleeping bag liner can be used to keep the inside your sleeping bag clean as well as to add additional warmth to your sleeping bag in cooler conditions. The Thermolite fleece liner can also be used as a stand alone summer sleeping bag, making it a versatile option for outdoor adventures and travelling abroad. The fleece liner comes in a mummy shape and is made from Thermolite material, which traps air inside the fibres of the liner to provide exceptional warmth. The liner weighs just 379g and packs into a compact ultra-sil stuff sack, with a pack size of 19 x 13cm. Equipped with a panelled draw cord hood for added warmth when required and a quarter zip for ease of use.
Last updated at 06/23/2026 10:18:00
Sea To Summit Thermolite Reactor Fleece Liner
Delivery $31.29
Sea To Summit Reactor Fleece Sleeping Bag Liner - Compact
Free delivery
Thermolite Reactor Fleece Liner
Free delivery between 1–7 July
originally posted on REI
This fleece liner is great for improving the warmth rating of sleeping bags and is definitely worth the extra space in your bag. I used the Sea to Summit Thermolite Reactor Fleece Liner to increase the warmth of my sleeping bag. I found it to be very soft and comfortable and enjoyed using it to sleep while on the trail. In addition, the packed size is small and at only 14.8oz it is worth carrying if there is any worry your sleeping bag may not be enough.I have seen some reviews say that it can be used as a summer sleeping bag. While that is not my intended use, I can absolutely picture someone doing that if they are interested in ultralight summer backpacking.
originally posted on seatosummitusa.com
Never new how much I needed a fleece liner and how much I'd actually use it. Already used it backpacking, car camping, and in hotels.It's great for when I'm on the road and trying to find the cheapest room possible I just throw all the provided blankets off the bed and curl up in this, keeps me comfy all night! Backpacking it helped me make my bag comfy down below freezing where I usually get cold around 35°. And car camping inside my rectangle bag when we were up at elevation surrounded by snow.Packs down extremely well and the zipper seems to be of quality which would be the only potential issue I see with it. The hood is nice to have as well! No complaints and I'm sure I'll use this for a long time. Fleece is the way to go
originally posted on seatosummitusa.com
Just got back from a 6 day trip. Going into questionable weather, I brought my new s2s fleece liner. Results were excellent. Adding more warmth on the cold nights and worked perfectly on top of my bag on the warmer nights. The fit works well for me at 5'7". The additional zipper is a welcome addition for a liner too! I usually run cold. So if you're like me, this is the liner to think about.
| Style | Reactor Fleece (78x28) |
| Insulation Material Type | Thermolite |
| Length | 0.17 metres |
| Shape | Mummy |
| Number of Pieces | 1 |
Sea To Summit Thermolite Reactor Fleece Liner
Delivery $31.29
Sea To Summit Reactor Fleece Sleeping Bag Liner - Compact
Free delivery
Thermolite Reactor Fleece Liner
Free delivery between 1–7 July
This fleece liner is great for improving the warmth rating of sleeping bags and is definitely worth the extra space in your bag. I used the Sea to Summit Thermolite Reactor Fleece Liner to increase the warmth of my sleeping bag. I found it to be very soft and comfortable and enjoyed using it to sleep while on the trail. In addition, the packed size is small and at only 14.8oz it is worth carrying if there is any worry your sleeping bag may not be enough.I have seen some reviews say that it can be used as a summer sleeping bag. While that is not my intended use, I can absolutely picture someone doing that if they are interested in ultralight summer backpacking.
Never new how much I needed a fleece liner and how much I'd actually use it. Already used it backpacking, car camping, and in hotels.It's great for when I'm on the road and trying to find the cheapest room possible I just throw all the provided blankets off the bed and curl up in this, keeps me comfy all night! Backpacking it helped me make my bag comfy down below freezing where I usually get cold around 35°. And car camping inside my rectangle bag when we were up at elevation surrounded by snow.Packs down extremely well and the zipper seems to be of quality which would be the only potential issue I see with it. The hood is nice to have as well! No complaints and I'm sure I'll use this for a long time. Fleece is the way to go
Just got back from a 6 day trip. Going into questionable weather, I brought my new s2s fleece liner. Results were excellent. Adding more warmth on the cold nights and worked perfectly on top of my bag on the warmer nights. The fit works well for me at 5'7". The additional zipper is a welcome addition for a liner too! I usually run cold. So if you're like me, this is the liner to think about.
I love the versatility that this liner adds to my sleep system. I also have the reactor liner that can add up to 14 degrees and a down sleeping bag with a comfort rating of about 40 degrees. I can mix and match liners and sleeping bag to get the temp rating that I want. I took the fleece liner and the sleeping bag on a recent trip to Havasupai in March where temps are unpredictable, and I was the perfect temperature while sleeping without having to bundle up in a bunch of extra clothes.
I've used STS liners as part of my sleep systems for years. Bought a Reactor recently to help beef up an older synthetic bag that has lost some of it's loft. Was impressed with increased warmth but, after experimenting, am feeling it added considerably to the bag's capacity but well south of 30 degrees. Also, the material is quite "sticky" so getting into the liner while wearing inner or mid layers, was a bit of a wrestle. That said, once situated, the liner felt super cushy and seemed to take up minimal space in the bag. I do a lot of moving around while sleeping and did not notice the liner tangling while flipping around. Here in NE, we get wild temp fluctuations so am particularly excited to use this liner as part of a super flexible system, on it's own, while ... MoreI've used STS liners as part of my sleep systems for years. Bought a Reactor recently to help beef up an older synthetic bag that has lost some of it's loft. Was impressed with increased warmth but, after experimenting, am feeling it added considerably to the bag's capacity but well south of 30 degrees. Also, the material is quite "sticky" so getting into the liner while wearing inner or mid layers, was a bit of a wrestle. That said, once situated, the liner felt super cushy and seemed to take up minimal space in the bag. I do a lot of moving around while sleeping and did not notice the liner tangling while flipping around. Here in NE, we get wild temp fluctuations so am particularly excited to use this liner as part of a super flexible system, on it's own, while covered with a sleeping bag (as a blanket) or inside a bag. Will certainly enable me to cut down on the number of sleeping bags I have had to stock.
Bought this sleeping bag liner to use with my -6c sleeping quilt. I camped with the combination with my Nemo tensor insulated in 0c temperatures. Definitely still felt some cold, especially in my feet. I don't know if I could say that it adds 18c of warmth in such temperatures.I think the rating might add 18c in a very controlled and specific circumstance. Either way, it helps and does add warmth. But when you're camping at 0c, I'd say it adds closer to 5c. It would vary by person.The liner compacts a lot smaller than I was expecting. About the size of a Nerf football and it is quite comfortable. The cut is pretty slim, so if you're a larger person, you might feel restricted in this. For reference I'm 5ft 5 and 135lbs and I felt like my feet were a bit restricted.
I have had the chance to try this liner out several nights. I have a top-quality UGQ 10* quilt however I am a VERY cold sleeper - I have thyroid trouble that contributes to it plus a naturally low body temp. I am TOASTY using this liner! It sort of pains me to have to add a pound to my pack but I am truly SO COMFORTABLE while using this liner and my sleep quality on trail has skyrocketed. Therefore, I've decided it is worth the weight penalty. I guess its good that I've spent ridiculous amounts of money on UL gear so that I can "afford" to have to carry this extra pound. I love the fleece - it feels very cozy and instantly warm - unlike a regular down cover that takes a while to trap the body heat to "warm up". It keeps my sleep system cleaner. I likening able to ... MoreI have had the chance to try this liner out several nights. I have a top-quality UGQ 10* quilt however I am a VERY cold sleeper - I have thyroid trouble that contributes to it plus a naturally low body temp. I am TOASTY using this liner! It sort of pains me to have to add a pound to my pack but I am truly SO COMFORTABLE while using this liner and my sleep quality on trail has skyrocketed. Therefore, I've decided it is worth the weight penalty. I guess its good that I've spent ridiculous amounts of money on UL gear so that I can "afford" to have to carry this extra pound. I love the fleece - it feels very cozy and instantly warm - unlike a regular down cover that takes a while to trap the body heat to "warm up". It keeps my sleep system cleaner. I likening able to easily wash this liner when I get off trail. I also like the versatility - Spring mountain temps can swing wildly and change quicklyon a multi-day - it's nice to be prepared for it all. I haven't yet had the opportunity to try this liner as a stand alone during warm months, but I look forward to trying it.
Cold sleeper here! I own a Western Mountaineering Uberlite 30 degree bag, which is super light but definitely not enough to keep me warm under 45 degrees. This fleece liner does the trick! I even made it through a night at 22 degrees (although with extra layers!!). The only drawback is the liner gets static when I wear my Wool layers, and since the zipper doesn't go all the way down you might find yourself somewhat "tangled" due to the fabric getting static-ey. Most importantly, it keeps me warm on those cold nights where I would otherwise have to invest in another, warmer and heavier sleeping bag. Good investment for me, 100%.
I have only used it once. It was 38 F , I slept in my car, I used it with my sleeping bag that is rated for cold weather, my bag is about 20 years old. I was warm until about 3:40 AM. Then I did get a little cold, though mostly from the waist down, I think it made a big difference in keeping me warm as when I felt the sleeping bag between the liner& the bag the bag was cold. For a reference I wore my base layer hiking clothes & hiking socks, next time I’ll wear some sweats as well.
I bought this to use in winter in my North Face One sleeping bag. It is very soft. It protects the sleeping bag from dirty socks, and it is washable like any other fleece material. Buying something durable was important for me. I have other products from this company, and they last a long time. Highly recommend this product.
| Style | Reactor Fleece (78x28) |
| Insulation Material Type | Thermolite |
| Length | 0.17 metres |
| Shape | Mummy |
| Number of Pieces | 1 |
