OK, I did temperature testing over the weekend. Don't laugh at my description, we're all scientists at my house.
Temperature readings were taken outside on the deck in my back yard on 12-11-2011. First the Bit Buddy insert was placed on top of a folded paper towel and heated in a Litton microwave oven for 60 seconds at 100% power. The insert was then placed inside the fleece cover and the Bit Buddy was wrapped around a lab thermometer. An initial temperature reading was taken at 10:38pm, but the reading had to be discarded as being incorrect because the experimenter did not give the thermometer enough time to come to an accurate reading. The Bit Buddy wrapped around the thermometer was then placed outside on top of a plastic bag covering an empty USPS regional rate box that had been set on the deck in the back yard. A dial thermometer normally used to measure refrigerator or freezer temperature was placed on the testing surface next to the Bit Buddy to measure the outdoor temperature. Readings were then taken at regular intervals.
For some reason the PDF file I created of the time and temperature data is too large to be uploaded here as an attachment, but I'd be happy to email you a copy if you'd like to see it. It took almost an hour (fifty-eight minutes to be exact) before the temperature inside the Bit Buddy had cooled to normal human body temperature, which of course is still warm enough to warm up a horse's bit. That was with the Bit Buddy in the open air; I'm confident that one would stay warm longer if kept in a coat pocket or some other small space that would hold in the warmth.