Sea to Summit  Thermolite Reactor Fleece Liner - Regular

Cold sleeper here! I own a Western Mountaineering Uberlite 30 degree bag, which is super light but definitely not enough to keep me warm under 45 degrees. This fleece liner does the trick! I even made it through a night at 22 degrees (although with extra layers!!). The only drawback is the liner gets static when I wear my Wool layers, and since the zipper doesn't go all the way down you might find yourself somewhat "tangled" due to the fabric getting static-ey. Most importantly, it keeps me warm on those cold nights where I would otherwise have to invest in another, warmer and heavier sleeping bag. Good investment for me, 100%.

I bought this a couple years ago since I tend to be a cold sleeper and wanted to upgrade my 30 degree bag for winter camping. It helps add about 10 degrees of warmth and I slept fine on a 20 degree night. What I like more about this liner is using it in the summer. This liner is great down to about 50 degrees with a base layer on and it's really nice since this is about the the size of half a loaf of bread. On the negative side, I am 6 foot tall and just barely fit in this and it is still a little uncomfortable so I usually sleep with my head out of the liner and wear a hat. It's also a really tight liner, so I found the need to stuff some clothes into my sleeping bag to fill a couple voids of dead air.

This fleece liner is great for improving the warmth rating of sleeping bags and is definitely worth the extra space in your bag. I used the Sea to Summit Thermolite Reactor Fleece Liner to increase the warmth of my sleeping bag. I found it to be very soft and comfortable and enjoyed using it to sleep while on the trail. In addition, the packed size is small and at only 14.8oz it is worth carrying if there is any worry your sleeping bag may not be enough. I have seen some reviews say that it can be used as a summer sleeping bag. While that is not my intended use, I can absolutely picture someone doing that if they are interested in ultralight summer backpacking.

I slept in my 15 degree sleeping bag with this liner and woke up to a -10 F morning. It was a comfortable night. I did have a good groundpad and I wore some of my layers

I have tried using the Reactor Plus in the past and did not feel any additional warmth. I then started to doubt the validity of thermolites efficiency and have since relied on the use of the SOL escape bivvy for additional warmth. Early 2016 I saw the new Thermolite Reactor Fleece and have used the reactor fleece on few outings both in wintery conditions at 28 F in march to add warmth to my 40 F Quilt and during this summer by itself down into the 60's. The Reactor Fleece certainly works. The material feels great next to skin and unlike the SOL Escape bivvy it won't make crinkly noises as you toss and turn. My issue with the product is that it is pricey and at 13 oz is a good 5 oz heavier and not as compact as the SOL Escape Bivvy. (Ultralight Guys will understand) The SOL Bivvy is also warmer. The two products when used in together is as warm as your standard summer down bag like those 45 F sleeping bags. It's a great product, but again it is on the pricey side.

I have had the chance to try this liner out several nights. I have a top-quality UGQ 10* quilt however I am a VERY cold sleeper - I have thyroid trouble that contributes to it plus a naturally low body temp. I am TOASTY using this liner! It sort of pains me to have to add a pound to my pack but I am truly SO COMFORTABLE while using this liner and my sleep quality on trail has skyrocketed. Therefore, I've decided it is worth the weight penalty. I guess its good that I've spent ridiculous amounts of money on UL gear so that I can "afford" to have to carry this extra pound. I love the fleece - it feels very cozy and instantly warm - unlike a regular down cover that takes a while to trap the body heat to "warm up". It keeps my sleep system cleaner. I likening able to easily wash this liner when I get off trail. I also like the versatility - Spring mountain temps can swing wildly and change quicklyon a multi-day - it's nice to be prepared for it all. I haven't yet had the opportunity to try this liner as a stand alone during warm months, but I look forward to trying it.

The material itself is warm. No doubt about it. I’m on my second with this product, as the first one’s draw string came off from one end on the first use. Also, the sleeve where the drawstring cord is threaded is made of a different material, which produces an annoying noise that’s amplified when the opening of the bag is closed around the face. Sounded like a mouse moving through a tunnel made of parchment paper too small for it. The fabric is okay. It’s got a slight waxy feel next to skin, otherwise incredibly warm.

This is a very nice bag liner and feels much smoother on your skin than a Cocoon. It also has a nice zipper which is an added bonus. I have used this four times now in differing temps from -10 to 60 and feel it doesn't not add as much of a temperature rating as it states. I used the layering formula of New Rating = Outer Bag Rating - (Inner Bag Rating/2) which has worked rather well for me over the years. All that said, still a good liner. I'm looking forward to using it as a stand alone summer bag when the times go above 80 or so. Just plan for a slightly lower rating on your outer bag than you might feel necessary. I gave four stars as the rating seems a bit off for me. Your feeling may be better depending on your gear and if you sleep warm or cold. Other than that, an excellent liner for adding warmth and keeping your sleeping bag clean(er).

Great addition to sleeping bag for cold/snowy weather. Only con is that it got easily tangled.

Super warm and cozy! Well made too, with a zipper that only goes down part way. It's not as comfy as the reactor extreme cause that liner sort of hugs you back, but this one is much warmer.