Sea to Summit Reactor Thermolite Liner

Editor: Cameron

Basic Description:

A light weight sleeping bag liner that improves your bags warmth rating and increases the life of your bag all while increasing user comfort.

Just the Facts:

Lighter weight, more packable than fleece
Adds up to 15 degrees F / 8 degrees C of warmth to a sleeping bag
Mummy shape with a box foot
Draw cord hood with mini cord lock
Color of liner is black
Weighs just 8.7oz
Packs into its own 3” x 5” sil nylon stuff sack



I have been researching sleeping bag liners for quite some time, and was looking for a way to improve the warmth of my old 3 season bag and squeeze a little more life out of it. I stumbled upon Sea to Summit which makes everything from liners, dry sacks, sleeping bags, and a lot of backpacking essentials to help organize and protect your gear. I decided on the Reactor Thermolite Liner because it was still lightweight and I was hoping to get some added warmth over your standard cotton or silk liner.
This liner is very comfortable, so much in fact that I was a little surprised. I expected this to be the one area that it did not shine at. I thought the material could have been itchy and not conducive to sleeping with it next to skin. I was wrong! I would buy this liner just for the added comfort in heart beat. It packs up so small and is so light that you could keep it in your sleeping bag and never know it was there until you crawled in at night. It has a nice synch cord at the top to keep the warm air in and cold air out.
Now for the testing of the claimed 15 degrees bag boost. I was sleeping in a cheap 30 degree sleeping bag on a closed cell foam pad with an R value rating of 2. The night I was testing the rating it was 34 degrees out, which was perfect to test the limit of my bag (which does not have its 30 degree rating anymore by the way). I slept in my sleeping bag with shorts and a t-shirt but no socks. I laid outside on my porch under the stars until my body became acclimated to the temperature. At this temperature I was not chilled in my bag but I was not warm either. I would honestly say I could have slept comfortably in my bag but again I was at the lower limit of the bag. Then, I went back inside my house warmed up to the same temperature as I was when I went out the first time and put the Reactor Thermolite Liner in my bag and ventured outside again. I then stayed out longer than before, and I can honestly say I never got to that point where I felt like if it dropped 5 degrees, I was going to be cold. You can definitely tell a warmth increase with this liner. Now for me to test the 15 degree bag boost claim I would have needed a very controlled environment or a colder night to test on and compare. I just didn’t get the colder night and probably won’t until next winter. Being conservative I would say it adds a good 5-10 degrees of added warmth. Without the liner my bag was a little cold on the inside and if I thought about it too much I would have gotten cold. With the liner installed my whole body was touching something warm.

Is this liner the solution to owning one 3 season bag for all 4 seasons and adding the liner when needed? I don’t think so, and I don’t think this was the intent of the company. But this liner is great for adding some warmth to your bag, increasing the comfort and keeping your bag clean and keeping your bag from getting warn out so quickly. I would definitely recommend this sleeping bag liner and will always have it in my bag when I am in the back country.

The people I feel could benefit the most from this sleeping bag liner or any that Sea to Summit offers is:
-Someone who has a high quality bag and uses it a lot and they want to limit the wear and tear to the inside of their bag.
-Someone who has an old bag that they want/need to get a little more warmth out of it for a special trip.
-Someone who needs to boost their old bags rating to squeeze a few more years out of it before upgrading their bag.
-Someone who just wants added comfort and a better night sleep.

What they could do better:

I don’t think they could do anything better, but the temperature rating increase is a little optimistic. I do feel this could be different for every user however.

Sea to Summit Reactor Thermolite Liner Review
  • Functionality
  • Value
  • Ergonomics
  • Durability

One Response

  1. Avatar for Editor Editor March 7, 2012