Did not work.
I tried one right after the purchase last October. When taking out the warm sticker, I could feel the solid clusters unevenly in the bag. Thinking it should be normal with the charcoal/carbon inside, I found the embarrasing bump in sweater on my back where I sticked it for a while, as all the clusters fell to the bottom of the bag. And the whole day the bag did not warm up at all. I was wondering whether I used it incorrectly and waiting for a second try on a cold day early this year. Unsurprisingly the same. There is a light stamp at the left seal supposed to be the manufacture date showing 2018.10.08 and the expiration date should last for 3 years, but I would suggest the seller checking with the manufacturer whether there was any package or shipment issue that made the charcoal/carbon activated already so they didn't work. Thanks.
Rating: 1 stars