When it gets really cold on your next overnight outdoor trip, you might find yourself reaching for a sleeping bag liner to add some extra warmth to your already warm sleeping bag. A good liner can add anywhere from 10 to 25 extra degrees to your sleeping bags effective temperature rating, providing much more warmth and comfort as the temperature drops. The most effective solution? The Sea to Summit Reactor Extreme.

Made with a 110 gm/2 Thermolite insulation, the Reactor Extreme can add a sold 25 degrees of extra insulation to your sleeping bag. Effectively, it takes a 0-degree bag and turns it into a -25F bag, or a 25 into a 0. For those of us who run cold, that’s a nice improvement and can sure make a difference in how comfortable you are falling asleep. It comes in a classic mummy shape with footbox, as well as a hood with drawcord and mini lock to keep it tightly closed.

The Thermolite insulation is hollow core, which means it traps in more air than regular insulation fibers. It’s also soft and stretchy, making it comfortable, moisture-wicking and perfect for using in nearly any weather. At 14 ounces, Sea to Summit compares it to a roll of paper towels, and it stuffs into its own Ultra-Sil stuff sack for convenient packing and stashing.

It’s our pick for the best Sleeping Bag Liner of 2018. With one of these in your pack, you’ll find yourself sleeping quite a bit more comfortably this winter.

Reactor Extreme Sea To Summit Liner Reactor Extreme Sea To Summit Liner 2