Bookwarmer

This would be like a cross between a dust-jacket and a hot water bottle that would make the book warm while you held it, for those cold nights when you're tucked up in bed with a good book.
It could be heated either using gel-pack inserts that are popped in the microwave beforehand for half a minute, or plugged in to the mains like an electric blanket. The outside would be soft or furry without being cumbersome to hold, and there would be a thin layer of insulation (silver foil etc) on the inside of the bookwarmer to prevent possible damage to the glue or bindings of the book.