Alex, I am talking real cold, middle of the winter Mt Washington, cold.
I carry a few "Grabber MyCoal - Mini-Mini Hand Warmers" (at 1.38oz for 2) with me always - anyway. They are great when your fingers get cold. Yes, I have great Mit's and liners but you know what they say about **** happens.
The cozy in the picture will also fit my Snow Peak 700ml Ti cup.