Gear Review: The Reactor from Sea to Summit

What is more exciting than getting ready for a great backpacking or camping trip? If you are like me, you enjoy planning all the details of the trip from packing, to choosing the route you will follow. Some find the packing to be stressful as they are concerned they will either not have enough gear or have too much gear. The amount of gear you carry in your pack is determined by the location, weather, and individual needs of the trip. So this brings us to the Reactor from Sea to Summit.

I know most of you would agree that needing something and not having it, especially when you are miles from civilization, can drain the fun out of any trip. One situation is not having the ability to have a comfortable and restful nights sleep. Another could be not having the ability to regulate temperature while you are shacked up in your tent for the evening. Both are undesirable scenarios for any trip. With that in mind, we decided to field test the Reactor to see if it could help alleviate these problems.


The Reactor is a sleeping bag liner (mummy shaped) made of Thermolite which is a breathable, hollow core fiber. Sea To Summit claims the Reactor will add up to 15 degrees Fahrenheit to your sleeping bag, or can be used alone in warm weather sleeping. The concept sounds good on paper, but lets see how it worked in a real-world test.


The Reactor in its home. The 3″ x 5″ nylon stuff sack.

Upon my initial inspection of the Reactor, I found it to be very light and compact. The Reactor comes in a 3” x 5” nylon stuff sack and all together weighs just under 9 ounces. The compact size is well welcomed as we are always looking for ways to lighten our load while being able to carry large amounts of gear. Out of the stuff sack, the Reactor is extremely lightweight and the Thermolite material is almost see through. The lining around the hood and stitching was very clean and neat. It does have a draw cord for the hood, so this goes hand in hand with your regular sleeping bag. I could see how the Reactor could be a complimentary fit to any sleeping bag. The Thermolite material was easy to compress and stow away in the nylon stuff sack. As always, the proof is in the pudding, so off to the trails we go.

It is funny because the Reactor is so small I could actually put it in one of the pockets of my cargo pants, But I decided to park it right next to my sleeping bag in my pack. So for the initial night with the Reactor, it was unseasonably warm. When it was time to call it a night, I laid out the Reactor in my +30 sleeping bag and slid right in. It was about 58 degrees out and within 5 to 7 minutes I was toasty. At about the 15 minute mark, it became stifling in the bag. I decide to open the bag and just lay in the Reactor. I cooled off, but not too much as it became comfortable. My body temperature remained consistent throughout the night. I was able to move around and even slept on my side without any issues. My feet had plenty of room and the hood came over my head easily. I felt very comfortable in the Reactor.


There is a flap keeping the Reactor dry inside.

If you do need to go to the rest room or anything, you will have to slip out of the liner as it does not have a zipper. I agree with this design as it saves weight and you keep the ability to wash it in your washing machine. You are able to hand or machine wash the Reactor in cold water as I see it could easily retain odors due to the material. I would suggest letting it air out like you would your sleeping bag. However you sleep in your bag, you can do the same in this liner.

I did have to try the Reactor without a sleeping bag and needless to say, it was very cool. At first it felt weird because the lightweight material almost makes you feel like you have nothing on, but it kept me warm throughout the evening. The temperature ranged between 70 to 75 degrees. So if you are going to be backpacking or camping in warm weather, you can save a lot of space in your pack by ditching the sleeping bag and only bringing the Reactor. Pretty cool to put your bed in your pocket. Now for what I found to be the Pros and Cons of this ultra lightweight, compact sleeping bag liner:


  1. Size – Takes up hardly any space
  2. Weight – Ridiculously lightweight
  3. Material – Keeps you warm as claimed
  4. Construction – Appears it will last as long as you take care of it


  1. No color choices other than black

There is plenty of room for a weary hiker.

As you can see, the Pros outweigh the Cons for the Reactor. We didn’t find any fault in Sea To Summit’s claim in the warmth Thermolite provides. It was comfortable both inside and outside of a sleep bag. The only suggestion I have is for additional color choices. I know some folks are picky about things, so just thought I would throw it out there. Though Sea To Summit doesn’t have the MSRP listed for the Reactor on their website, the average cost from authorized dealers is around $55.00. This is not bad for something that can take the place of a sleeping bag. Also thinking outside the box is the Reactor would be great for your BOB or get home bag.

Reactor 6

This large liner fits in this small sack. Awesome!!

In conclusion, the Reactor is a great product. If you are going to be doing some serious backpacking or camping in a place where the weather could change on you; the Reactor can be an added piece of insurance that won’t break your back or the bank.

Stay safe out there!!


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