Heated sleeping bag liner,Travel and Camping Sheet, Pocket-Size, Lightweight, 100% cotton flannel fabric, special metal heating plate with Maximum Power 9W, USB interface

This Very thin bag liner has the controls under your shoulder. As soon as you move you changes the settings. It also Eats the battery very quickly. I have a large battery pack and it only lasted a few hours ( heat setting irrelevant as you sleep on the control)

Battery packs wont keep this going for long, I get super cold sleeping and was in a -0 C bag. This was just a waste of space. Hard to get into, and not very warm anyways. I would buy a good pad or good sleeping bag liner with the money from this.

Fits my zempire monstamat king single sleeping mat like it was made for it (198cm X 76cm)Powered by Anker power bank on high setting for 8 hrs.Covered by halcyondreams 700gsm pure opulence wool quilt and was comforfably warm camping in zero degrees.

pretty warm when you set it on high, I wish they will produce one with the heating element on the top also, so both top and bottom element would wrap you up and you'll feel toasty during the cold time.

I'd rate it 3 1/2 if I could. It'd be a 4 if it was a little longer.I've only tested it once so far. The temperature dropped to 27F, but I was able to sleep comfortably. I found the heating elements work surprisingly well. The heating element on the torso area seems the warmest, but it could be due to better body contact compared to the legs. A mummy bag shape to the liner would help. I tested it in a rectangular sleeping bag so using it in a mummy bag would also help.The temperature dropped to 27 F, yet I stayed warm enough to sleep comfortably. My 10000 mAh battery pack lasted the whole night also. I had enough power left in my battery pack to go a second night.Overall, I am pleased. It does need to be a little longer. I'm 5'11" and isn't quite long enough for me. I am also happy my battery pack should be large enough to last two nights. I could likely get the the same effect using disposable chemical warming packs. I am amazed this works as well as it does using a 10000 mAh battery pack. I'll be sure and edit my review after I've had more opportunities to test it.