The Butterfly has been discontinued. If you're looking for something new, check out the best sleeping bag liners for 2020.
Historic Range: $24.93
Reviewers Paid: $35.00
Maybe one of the best things I've ever stumbled upon! Went camping a few weeks back in below 20 degree temps. Hey, no problem I got an external framer just chunk some more stuff inside and strap more out.
So that meant I brought a fleece blanket that weighs damn near close to the same as this "liner", and enough clothes for a refugee camp in Siberia. Long story short, I was plenty warm in my 32 degree bag + blanket + 2 LJs, Cords, and soccer warm up pants + about same set up for upper body.
Now I have an internal frame (gotta make the switch at some point for certain hikes where externals extra weight is a pain), and thus I lost a bit of room with it...ENTER the Butterfly! With a compression sack (I use Granite Gear Air Compressor) packs down to about the size of a novelty basketball (those little ones). Amazingly warm inside of another bag! I estimate around a 10 degree or more rise for your bag's temp rating! Very roomy, however I should mention I'm 5'8" and around 140 so I don't take up much room anyhoo.
Now, best part is not only do you get a "liner" for $35 that weighs only a pound (yea suckyness, thus the 4 star rating) more than other liners, you also get a real sleeping bag for those trips in the summer time to early fall. Basically I would have been a little wary at $50+, but for 35 hell, even if it hadn't worked well as a liner it still makes for one cheap but well crafted summer sack!
Temperature Rating: 50F +
Weight: 1.1 lbs
Price Paid: $35