I don't often wax lyrical about a product - BUT these are lovely - thermal fleece insoles to put in your boots for winter by a company called Boston.
I got mine in Waitrose; they are only just over £2 and I love them. They make the soles feel really comfortable, but even better my feet are warm (but not sweaty!!)
They even passed the ultimate test of two hours standing on a football touchline in the cold.
www.bostonshoecare.com/sulor/index.php