It actually does work!
I bought this liner on a whim to keep my bags (and my little son's) clean. It turns out that this thin little "baggy" actually does add a bit of heat retention. I was pleasantly surprised that it actually kept me warmer than I'd thought, even though I still plan to buy a warmer liner so I don't need to buy a more expensive bag.
I'm a bit confused why the call it CoolMax... I expected it'd only be good to keep the bag clean and absorb sweat when it's hot, but it actually does more. Unfortunately, I didn't have it along when I really needed it on the PCT during a storm at 32.5 degrees, so I can't comment on how it performs when wet (EVERYTHING was wet, even the tent was raining on the inside).
The material appears pretty thin and sensitive, and I imagine it'd be pretty easy to rip it, but I'm pretty careful and haven't had an issue yet. Some folks complain that the only way in is from the top, so here's what I do: I carefully put the liner on like a pair of pants (but up under my shoulders), then I slip into my bag like everyone else, and then sit up and adjust the liner and then the bag. No problems for me.
I Love This Bag!
I love this little thing. At first I thought it was too flimsy; however, I beat the snot out of it and its still hanging in there!
1) This saved me in my Cat's Meow for two reasons. First, it gave me added warmth when the temps dropped and second, it kept my stink off the bag. No other way to put it: when you are showerless for several days and in the same clothes...this little bag will protect your much more expensive sleeping bag from your reek.
2) Light and easy to shove in your pack - can't say anymore there.
3) Was great for climbing into in the middle of the day when I wanted to read my book but it wasn't super cold out. I look forward to using this around my house in the winter.
The only con I could think of (but didn't warrant ditching the 5 stars):
You can't move around in it much. Since that isn't what I bought it for, that wasn't a consideration for me. I thought I should mention it though, as it might be a factor for someone else.
Great for extra warmth!
Will not go into the cold woods without this item! It makes my +20 degree bag really +20 degrees! If you like to sleep in your briefs and not all your clothing this item will help you do that.
I started off a night in my briefs with temps in upper 30s. Around 3am the temp dropped to 26 degrees. I woke up some what chilled in my NF +20 synthetic bag. I slipped into the liner and stayed in just my briefs to see how it worked. WOW! I was toasty warm the rest of the night.
It's also nice to not have to slip into that cold nylon either.
Can't wait to use it for hot days instead of a big sleeping bag here in Texas.
If you sleep kind of cold, GET THIS ITEM! You will love it!
Does what it's supposed to
We bought this liner for my down mummy bag, with the primary purpose of keeping the bag clean. As an added bonus, it also adds a couple of degrees to the bag's warmth. When the weather was too warm to be zipped in the down bag, the liner was the perfect lightweight blanket. It washed well after use, and seems to be good to go for the next trip. The material is a little thin, so I'm not sure how it will hold up over time, but so far, I'm very happy with it.
I love this thing
Very nice liner. I bought this last minute as I had planned an early Spring camping trip and the temperature took a turn on me. I was afraid the 30 degree bag I had wouldn't be enough so I bought this. The liner made my mummy bag warmer and much more comfortable. Also it is easier to wash than trying to wash an entire mummy bag. I've used it twice now and can't believe I went this long without one. Packs up nice and tight for cramming in a backpack.
Great Comfort for a low price
I bought this product before heading out on a snow camping trip in my cat's meow sleeping bag, which is only rated to 20*F. I have to say that I would have been really uncomfortable without this. I'm amazed at how much heat and comfort can be contained with such a thin layer of fabric! It packs down pretty small and can be stuffed anywhere in a pack.
I would buy this again, and definitely recommend it!
Keeps the bag clean, adds warmth
Bought two of these before we went on a month long road trip with 2/3 of the nights sleeping in this liner and a sleeping bag. The liner is very soft and comfortable and helped keep the bags clean! It's much easier to just toss the liner in the wash than the bag itself, so we could launder them in the middle of the long trip if they became stinky.
Clean bag, comfy sleep
I regularly use sleeping bag liners, primarily to help keep my bags clean. This liner is very comfortable, stretching and comforming easily if tossing and turning is the order of the night. Have also used it by itself on warm summer nights. I would like to see an option for some kind of side opening. Climbing in or out from the top can be a little awkward.
I found this liner to be a great summer bag for early night time, offering a little coverage without making me sweat. It also turned out to double as a superb mosquito netting, though I suppose you could find a lighter net. I was happy with it in my average-weight pack, but I may rethink when I go UL.
A must have
On a hot sticky midwestern night, this liner makes a world of difference. I start out in just the liner and as the night and I both cool off, I slide into my bag.
The liner moves with me, and gives me the most comfortable night in a bag I can remember.