There’s no shame in kitting yourself out with a winter-busting thermal under-layer. Heck, if it’s good enough for granddad, it’s good enough for you – and it’ll save on the heating bill. But unlike thermals of old, today's toasty undies fit like a dream, and no one need know you’re wearing ‘em. Just take a look at the video below, and learn how to keep warm covertly this January.