Sea to Summit Reactor Sleeping Bag Liner Review

Overall Rating: 9/10

The Thermolite Reactor liner from Sea to Summit provides an ample amount of warmth while still being breathable. Even though this sleeping bag liner is marketed towards those sleeping in cold conditions, I find it versatile enough to use in temperate climates as well. The fabric is so comfortable and livable that I also bring get good use out of it for car camping trips as well.


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  • Adds up to 15 degrees of warmth

  • Soft and cozy fabric

  • Wicks moisture and doesn't feel clammy

  • Versatile for many uses


  • Slightly bulky when packed up

  • Can be too warm for warm nights/hot sleepers

  • A bit of extra material for my small frame

  • Can still get static-y


Why Use a Sleeping Bag Liner?

If you don't currently use a liner, you should! I went a couple years before investing in one, and now I refuse to sleep in any sleeping bag without one. Some reasons to always use a liner:

1. Keeps your sleeping bag clean
You likely spent a pretty penny on your new sleeping bag, so you probably want to treat your bag well to make sure it is going to last a while and keep you warm. You might not realize it, but the oils and dust on your skin can seep through the fabric and diminish the quality of the bag over time.

2. Easy to clean
I'll be the first to admit, I've never cleaned a sleeping bag. Don't judge me! I'm just lazy and don't want to ruin the bag by washing it incorrectly. With a liner, I can get as dirty as I want in the backcountry and still climb into my bag at the end of the day without having to feel guilty. Washing the liner is then easy as throwing it into the washer at home!

3. Keeps me warm
My number one reason for using a liner is to give me a little extra warmth at night. I'm a cold sleeper, so making sure I'm warm enough to get a good night's rest is important to me.

4. Regulate your temperature
Do you find yourself constantly alternating between suffocatingly hot and then freezing cold? I feel like when I use a quality liner, the material does a good job of wicking any sweat and preventing me from feeling like a clammy worm inside of a candy wrapper. It took me a while to fine tune my perfect sleeping system and clothing layers over the years, and the liner is a big part of it for me.

5. Makes for the perfect light layer
If you find yourself traveling or sleeping in an extremely hot climate, you can always just use a liner as your only layer. Personally, a silk liner alone would be a little too light and cold for me, but I find this warmer one has just the right amount of weight to sleep in on its own.


Warmth & Breathability

My favorite thing about the Sea to Summit Thermolite Reactor Liner is that it provides the much needed extra warmth, but is versatile to use in a variety of conditions since it doesn't overheat as much as you'd think. I've tried out this liner on camping trips in moderate temperatures as well, and I was pleasantly surprised to find I didn't overheat.

The material does a great job at wicking any sweat away while still being breathable enough to not cause overheating. Obviously I wouldn't recommend using this bag in very warm climates, but I do find that this liner is usable in a wide variety of temperatures outside of just extreme cold, and this liner is my go to for backpacking as well as car camping trips.


Comparison to Other Liners

I started off with a Cocoon silk liner I picked up off Craigslist (I know, I know.. I was in college!), and it worked fine. I did experience several cold nights that could have also been due to my sleeping bag and/or sleeping pad, but I decided to finally upgrade to a warmer liner. I loved the Sea to Summit Reactor Thermolite Liner from the first time I tried it.

The Thermolite Reactor does pack larger than the other silk liners, but I think the added warmth is worth it. I also felt like the material of the Sea to Summit Reactor Liner is much more comfortable than the Cocoon, and so moving forward I'll definitely be replacing my Cocoon with this one.


Size & Weight

Weighing 8.1 ounces and being just slightly larger than a soda can, the liner is not the most ultralight. It's still light enough for me to pack on all of my backpacking trips no matter if I'm headed into the mountains or to the desert (it can still get cold at night in the desert!). I take sleep very seriously, and my desire to make sure I'm warm enough at night is strong enough to justify packing it on most of my trips.

I also think the warmth per ounce and size is one of the best you can find on the market.

A range of Sea to Summit's gear for size comparisons from left to right:  Aeros Premium Pillow ,  Reactor Liner ,  Comfort Light Insulated Mat ,  Spark III sleeping bag

A range of Sea to Summit's gear for size comparisons from left to right: Aeros Premium Pillow, Reactor Liner, Comfort Light Insulated Mat, Spark III sleeping bag



Another one of my favorite things about the Sea to Summit Reactor Liner is how nice the material feels against my skin. I now get excited to climb into my sleeping bag and curl up in the material. Unlike other sleeping bag liners, I don't get as tangled in this liner or accumulate an extreme amount of static inside from moving around.

Comparing the different fabrics of the liners. From left to right:  Cocoon Silk Mummy Liner ,  Sea to Summit Thermolite Reactor Liner ,  Sea to Summit Premium Silk Liner .

Comparing the different fabrics of the liners. From left to right: Cocoon Silk Mummy Liner, Sea to Summit Thermolite Reactor Liner, Sea to Summit Premium Silk Liner.


Final Thoughts

The Sea to Summit Thermolite Reactor Liner is now my go to sleeping bag liner for 90% of my camping/backpacking trips. I really love that it gives me the extra warmth I sometimes need, but while somehow not making me too warm when it isn't as cold out. And even if the nights get really warm, I can always sleep in just the liner itself or unzip the bag. The only time I would opt against packing it would be for ultralight trips, or for very extreme weather situations (think jungle or scorching desert).

Although on the heavier/larger size of the sleeping bag liner spectrum, I think the liner provides a great value of comfort and warmth. Especially for the price point, I think it's a great liner to at least test out to see if it will improve your outdoor sleep system.

Check out what my go-to pieces of gear are!


Disclaimer: This is not a sponsored post. I selected the product to receive it for review, and these are all my original opinions. This post does contain some affiliate links. What this means is I might receive a portion of the sales, at no cost to you. If you choose use them, thank you for your continued support of this blog!