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Reviews > Sleep Gear > Summer Bags and Liners > Sea To Summit Reactor Thermolite > Owner Review by Kathleen Waters


June 21, 2014



NAME: Kathleen Waters
EMAIL: kathy at backpackgeartest dot com
AGE: 63
LOCATION: Canon City, Colorado, USA
HEIGHT: 5' 4" (1.60 m)
WEIGHT: 125 lb (56.70 kg)

Living in Colorado and being self-employed, I have ample opportunities to backpack. There are over 700,000 acres/280,000 hectares of public land bordering my 71-acre/29-hectare "backyard" in addition to all the other gorgeous locations which abound in Colorado. Over the past 15 years, my husband John and I have also had the good fortune to hike/snowshoe glaciers, rain forests, mountains and deserts in exotic locations, including New Zealand, Iceland, Costa Rica, Slovenia and Death Valley. My hiking style is comfortable, aiming for lightweight. I use a tent (rainfly if needed). Current pack averages 25 lb (11 kg) excluding food and water.


Manufacturer: Sea to Summit
Year of Manufacture: 2014
Manufacturer's Website:
Listed Weight: 8.1 oz (0.23 kg)
Measured Weight: 8 oz (0.23 g)
Reported Dimensions: 82 x 35 in (208 x 89 cm)
Measured Dimensions: 78 x 35 in (198 x 89 cm) from bottom to top of "hood" x widest part at "neck"
Measured Dimensions: 14 in wide (36 cm) at toe box and 65 in (165 cm) from bottom to widest part at "neck"
Reported Stuff Sack Size: 3 x 5 in (8 x 12 cm)
Measured Stuff Sack Size: 4 x 5 in (10 x 12 cm)

Other details: (From Manufacturer's Specifications)

Sleeping Bag Shape: Mummy with foot box
Draw cord hood with mini cord lock
Added warmth (F): Up to 15 degrees
Added warmth (C): Up to 8.3 degrees

Material: Polyester (liner) Nylon (stuff sack)
Liner Color: Black


Reactor Thermolite Liner
Picture Courtesy of Sea to Summit


I've always thought of sleeping bag liners as being something to just keep the inside of a sleeping bag a little cleaner - something to absorb some sweat, rub off some of the day's dirt, and such. I never purchased a liner because, hey, I don't stink! Yeah, right. Whatever! I don't want to add any more weight to my pack than I absolutely must.

So, when I saw the Sea to Summit Reactor Thermolite Mummy Sleeping Bag Liner, I was not all that interested. Sure, it's pretty small and weighs very little, but was it necessary? Not to me. However, after chatting with some friends, I came to realize I could maybe, on many backpacks, ditch my heavier weight (bulkier) cold weather sleeping bag and carry my way-more-compressible, lightweight summer sleeping bag with a liner and save room in my pack plus save a couple of ounces/grams (3 oz/85 g to be exact) besides. Not to mention, I could admit to being maybe a little trail-dirty and wanting a cleaner bed and save my sleeping bag from a cleaning or two!

That was back in late fall of 2013 and I'm so happy I joined the Sleeping Bag Liner Aficionados Club!

Since then, I used the Reactor liner at least a dozen times in all sorts of locations and conditions.

Over these past 8 months, many of my nights using the Reactor liner took place in south central Colorado in the approximately 100,000 acres (40,468 hectares) of Bureau of Land Management (BLM) land encompassing the Cooper Mountain range/Royal Gorge area near Canon City or the Wet Mountains south of the Arkansas River Valley.

The Cooper Mountain range is mostly piņon pine and juniper-covered high desert with rough primitive game and mining trails (for the most part) and is easily accessed just outside of my property fence line.

The Wet Mountains rise up from the Arkansas River Valley and are dense ponderosa pine and sage forests.

Elevations of the locations where I slept in the liner, ranged from 5000' up to almost 14000' (1524 m to 4267 m) and temperatures at night varied from 17 F to 56 F (-8 C to 13 C).

Out of state locations where I camped-out included a 5-day trip to the Superstition Mountains in Arizona (east of Phoenix) in early May and my most recent trip to the Great Sand Dunes National Park and Preserve for two nights in mid-June.
Great Sand Dunes Campsite
Dexter guarding my Reactor liner in tent at right!
Liner in sleeping bag
Reactor Liner in my sleeping bag at Great Sand Dunes NP

I experienced mostly beautiful cold to mild weather in Colorado on outings during this time period. The Superstition Mountains were hot in the sun, but cold at night and the Great Sand Dunes National Park and Preserve trip could be summed up with one word - WINDY!

OK, that covers the "field locations and conditions" part of this review, now for the results.

Water bottle vs liner size comparision
Petite Reactor Stuff Sack
First off, as I stated above, the Reactor liner packs down quite small into its own stuff sack. As you can see in the picture at left, we are talking about a package that is about half the height of a 1 L water bottle and an inch (2.5 cm) more rotund. The stuff sack easily opens and closes tight via a very small barrel locking system and there is a flap inside the stuff sack to further keep out the elements. Thankfully, the Reactor liner folds very neatly with no fuss and actually fits BACK into the stuff sack.

Once removed from the stuff sack, the Reactor liner stretches out fully to its very generous length and width. There is even a curved top adjustable (via a drawcord) hood section to cinch down, but I never used that feature. I never cinch down the hoods on my sleeping bags either as I find it too constricting. If I need more head warmth, I'd rather wear a knit cap.

The Reactor is amazingly smooth and the knit material feels amazingly soft. Very, very cozy! I love sliding into it after a long (or short) day on the trail. I usually wear long or short, silk or wool base layers to sleep in depending on the temperatures outside and both fabrics work well with the liner. Only once and that was on the first night of my most recent trip to the Great Sand Dunes National Park and Preserve, did I have a problem with my base layer bottoms in the liner. The pants were a heavy brushed fleece material and they "stuck" to the liner causing me grief until I finally stripped the bottoms off after which I slept bare-legged in the liner quite comfortably.

As to the warmth-adding features of the Reactor, I can't quantitatively define how warm I was using the liner versus if I had not used the liner as conditions changed from one use to the other. I can say I was definitely comfortable and did not awaken because I was cold any night I did use the liner in similar situations. For example, the first night I was in the Superstition Mountains in Arizona, I darn near froze to death and with chattering teeth and goose bumps, had to get up and put on a fleece jacket and a knit cap. I didn't have the liner in my sleeping bag and was too lazy (and didn't want to wake my granddaughter up) to dig in my backpack to get the liner. I, erroneously, thought Arizona would be warmer at night, since it was over 100 F (38 C) during the daytime. Hah! The next night I was ready with the liner completely inserted in my sleeping bag and I slept like a baby sans extra layers of fleece.

On the second night of my last outing at the Sand Dunes, I was warm enough to leave my sleeping bag totally unzipped and flung open, having only the Reactor liner covering me for most of the night. Only in the wee dawn hours when the wind really started to whip through the trees, did I pull my sleeping bag back over me for a little more warmth from the resultant chill. I wore lightweight wool base layers that night.

I haven't had many problems with getting twisted in the liner when I sleep except when wearing the abovementioned offending base bottoms. I've found if I take the time to properly stretch out and insert the liner in my sleeping bag, I'm good for the night. However, on the rare occasions that I might be dreaming I'm running from that brown bear, or floundering down the raging Arkansas River, I end up wrapped in the liner like an Egyptian mummy!

Though the Reactor liner doesn't seem to hold onto sunscreen, bug spray or smoke odors (as I said before "I" don't stink!), and I really haven't detected any staining, I have washed the liner several times now. To wash it, I turn the liner inside-out and toss it in my front-loading washer with regular detergent, no bleach and no fabric softener with the rest of my technical gear. Using cold water and a wool/hand wash cycle, I've found the liner to come out of the wash beautifully. I have even dried it in an electric dryer though I prefer to hang it outside in the shade. I love a fresh air-dried clothing smell! The Reactor hasn't stretched out, nor has it become shrunken. So far, there are no pulls, unraveled seams, pilling or fading. I'm planning on it lasting a long, long time and spending many comfortable nights under the stars!


1.) So soft and cuddly against my skin.
2.) Really does add warmth to my sleeping bags.
3.) Wears and washes well.
4.) Takes up minimal space and adds little weight to my pack.


1.) Can become twisted and constricting if I'm sleeping restlessly.


Good things come in small packages, they say, and the Sea to Summit Reactor Thermolite mummy bag liner certainly gives truth to that old adage! This is one item, I never thought I would ever use, but I am now a believer in liners and won't be leaving this one behind anytime soon. I've found I can cram a smidgen more in my backpack now, but more importantly, I sleep better in camp. A good night's sleep after a good day's hike is not a luxury anymore! This is definitely a keeper!

Kathleen (Kathy) Waters

This report was created with the Report Writer Version 1.5 Copyright 2014. All rights reserved.

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