I had such high hopes for this product. The Reactor Extreme is a ThermoLite sleeping bag liner and the label indicates that it can add up to 25°F of warmth to your sleeping bag. These liners have a shelf price around $65. My purpose for buying the liner was:

• Use it as a very light sleeping bag in very warm summer weather
• Augment my normal sleeping bag in seriously cold conditions
• Use it in conjunction with an emergency space blanket bivy in my Bugout Bag

I tried the liner at home first. I keep my bedroom pretty cool at probably about 60°. I tried sleeping on the top of my bed using only the liner. It was not nearly warm enough. The material is thinner than many of my T-shirts and it felt about as warm as a single bedsheet (perhaps a thin flannel sheet). I was hoping that it would be much warmer. On the second night I slept under my bed comforter only. I woke up at night and then slept under the comforter and in the liner. I did not feel any warmth differences when I used the liner.

There are many advantages to using a sleeping bag liner. If you are sweaty and dirty then the liner will take the brunt of your untidiness and you can easily wash it. It should also provide added warmth. I had another liner many years ago and it was larger but you could definitely feel the warmth difference. The Reactor was a complete disappointment but with performance and especially with price. I would venture to guess that a cheap, compressible fleece blanket would provide much better performance than the Reactor. I read other online reviews that gave the Reactor a high score but my experience was just the opposite.

The Reactor Extreme is made of very soft and comfortable material. However, I do NOT recommend it because it is expensive and I feel no appreciable warmth difference. If you are a hot sleeper then perhaps this product might work for you. For me this liner was about as effective as a single-ply bedsheet. I read positive online reviews of this product but my experience with it was not positive.