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Thermolite Reactor Extreme Liner
The THERMOLITE Reactor Extreme is the warmest backpacking knit sleeping bag liner we offer. The hollow fiber threads work just like the hollow fur of a polar bear in that they trap heat effectively. When the mercury drops you'll appreciate the mummy shape and drawcord hood with mini cord lock attached. Depending on your environment and sleep conditions, this liner can increase your sleeping bag warmth by up to 25F.
THERMOLITE FABRIC
The Reactor Series Sleeping bag liners and the foot boxes of the Women’s Trek, Talus and Latitude Sleeping Bags use hollow core THERMOLITE fiber to add warmth. Hollow cores fibers trap extra air for insulation (just like the hollow-cores of polar bear or caribou fur). Knitted THERMOLITE fabric is soft and stretchy and comes in three different weights: 80g/m² fabric used in the Reactor and the underside of the Compact Plus liners; a 110g/m² fabric which is used in the Extreme, and the core and foot box of the Compact Plus liner; and the Fleece, the warmest of all the fabrics.
HIGHLIGHTS
Packed Size Comparison:
Similar to a red cup that is solo.
Weight:
14 oz ≈ Lighter than a roll of paper towels. Warmth:
Adds up to 25°F to the temperature range of your sleeping bag.
BONUS:
Easy to wash and helps to keep your down bag cleaner for longer.
Viswa Viswanathan
Reviewed in the United States on February 23, 2025
I bought this for Everest Base Camp trip and I used this every night. Our guiding company gave me a sleeping bag but I felt more comfortable getting into this liner first and then the sleeping bag. This liner definitely added more warmth. I also used it later during our camper van trip in New Zealand on chilly nights.
Deborah Bonin
Reviewed in the United States on January 18, 2025
Cozy, warm and comfortable.
GUTI
Reviewed in Spain on July 2, 2024
Excelente para dormir en interiores o como saco interno para días o lugares fríos
R. Cooper
Reviewed in the United States on July 9, 2023
This SeatoSummit product performs very well, and may be the best money I've spent as I figure out products that work well for me. I'm 6' 2.5" inches tall/260 lbs, camp 10-12 times per year, and have been trying to survive colder temps by augmenting my Army patrol bag that is part of the original "sleep system". It is rated for 30 degrees survival. I use an R7 rated sleep pad from Costco with the bag and this liner. The patrol bag is about two inches too short for me to have over my head with any flexibility, so I really feel the cold around my shoulders when the liner slips off my shoulders below my chest. When I wake up from the chill and pull the liner back up to my neck, it's instant warmth,...an easy extra 10 degrees in heat retention. The only improvement I could recommend is perhaps a more robust draw string for when you get into the liner, so that is doesn't slip down if you toss in your sleep.
Customer
Reviewed in the United States on April 23, 2023
Really satisfied with the feel of the material, the durability, and effectiveness of the bag liner. I got the extreme version because I wanted to be able to pair it with my 20° bag and get more range and extend its life. I also planned to use the bag liner as a hot summer night sleeping bag. It’s also much easier to wash than a sleeping bag. So it’s nice to use on trip you might be rolling a little grubby.Turns out my favorites use for it is as a summer bag. It’s very small when packed compared to a sleeping bag and works well to keep you comfortable on a backpacking or bikepacking trip on warm nights. It also works well as a bag protector with added warmth to my -20° winter bag. Allowing you to sleep without base layers if that’s your thing.It does not however extended the range of my 20° bag. So if you’re thinking to buy this to push your 20-30° bag to a 0° then I suggest putting them money towards a proper 0° instead. Sleeping outside in zero degrees is really cold and while this helps a bit, it doesn’t make up for the right gear for the job.
Alice H
Reviewed in France on April 1, 2023
Texture très agréable contre la peau, fait effectivement gagner un ou deux degrés en thermie. Large, parfait pour ceux qui se tortillent la nuit.
Tusse Lago
Reviewed in Sweden on June 1, 2021
Jag köpte en liner efter mycket funderande och valet föll på denna lite av en slump, men jag är väldigt nöjd med mitt köp. Materialet är behaglig och den adderar värme på ett bra sätt. När jag har använt den har jag haft en förhållandevis tun sovsäck som jag nästan haft helt stängd. Genom att täcka hela eller delar av kroppen med linern så är det lätt att variera värmen även om det finns mygg eller annat som man vill stänga ute. Den största fördelen är dock att användningsområdet för befintliga sovsäckar utökas. Jag tror att Carinthia Defence 1 och denna liner skulle kunna vara en riktigt bra kombination.
Cindarella
Reviewed in Germany on December 20, 2020
Super feiner und bequemer sleepingbag, dachte zuerst das es nicht fein ist ein tuch im schlafsack zu haben, aber man spührt es kaum und es wird echt fein warm darin, noch nicht draußen getestet aber ich freue mich darauf. Sehr kompakt und klein.
ktrenholm
Reviewed in Canada on January 28, 2020
Surprisingly awesome. Very thin, but added a good deal of warmth to my bag. I used it in a hanging bivvy with a summer bag and was able to actually catch some Z’s.
MPKNYC
Reviewed in the United States on January 23, 2013
I really appreciated this liner as the temp fell from 20 degrees to 3 degrees overnight this weekend in the Catskills. Normally I would be very uncomfortable in my 15 degree bag at these temps, but the liner made it noticeably warmer. One of the reasons is that is eliminated the natural cold spots you get in a bag when not occupied by your body while you sleep, so when you shift you normally feel the cold. With the liner, which was snugly wrapped all around my entire body all night, I slept very well with no cold spots. It is big enough to provide room to shift positions but stays with you all night.Is this liner (or any liner for that matter) perfect for every sleeper? Of course not, but with the right layering and a halfway decent bag it really does make a difference and keeps the bag much cleaner. Small and easy to pack. I will be taking this with my on all cold weather situations.My recommendation is give it a try and see if it works for you. Cold weather sleeping is all about finding a layering system that works for you. This is a great additional layer that worked very well for me.
Studio Gear Head
Reviewed in the United States on June 3, 2012
I paid such a ridiculously high price for this product that I am too ashamed and embarassed to admit it, to you. I did, however, decide to purchase it, anyway, despite the high premium. Here is why ... So, I have constructed a lightweight 3-season system, for Central Texas, which does get "very" cold, at unpredictable intervals, throughout the late-fall to early-spring "trimester". Central Texas is Hill-Country ... Lots of steep ridges and canyons, all bunched together and there is lots of climbing involved and major weather fronts converge, in this region, manifesting all sorts of conditions, sporadically and unpredictably. My sleep-system consists of ONE G.I. Gortex Bivy-Bag and one SnugPak compact and lightweight "JUNGLE" bag (with integral bug-net), ... In order to augment this basic system, I also carry a VERY light and VERY compact Adventure Medical ThermoLite 2.0 Reflective Emergency Bivy AND ... YES ... This (equally ultra-light and compact) ThermoLite Reactor Extreme Mummy Liner. In colder weather, I may carry an additional silk or fleece bag liner. *** COST JUSTIFICATION *** These augmentation components fit in your open hand, and are smaller than a standdard roll of toilet-paper (and are a little lighter.) This allows for a very light, compact, and highly mobile and flexible sleep system that can "stretch" your temperature tolerance by (very hopefully) 25 to 30 degrees, F. I also carry a Short RidgeRest (aluminized) closed-cell pad, which is shorter and narrower than most pads. To be honest, I do not believe that these (ThermoLite) ultralight options perform to their optimistic claims, of 15 degrees for the thermal bivy and 25 degrees for the Reactor-Extreme bag liner ... Again, used together, properly, ?? ... 30 degrees of boost is the most one could hope for, and is probably overly optimistic ... I would expect to get slightly better than 20 degrees using BOTH thermalite components, if the temps were below freezing. Anything that weighs less than a roll of toilet-paper and is smaller, that can boost my sleep comfort (and survival envelope) by ANY significant amount MUST be worth spending a bit "more". ... And ... I sure DID ! Sorry ... no anecdotal gripes, as of yet ... I try not to use this resource any more than necessary. If I KNOW ... IN ADVANCE ... That it will be cold, then I will pack my USGI-ECWS-IMSS which is 12 pounds and will handle anything Texas can throw at me (any time).Hope this helps.
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