Quick clarification before we go any further: we are talking about the rubber ones on your feet, not the ones in your top drawer. If you are not from the Antipodes, that may need saying twice. Right, now that is sorted. Summer is not here yet. But it is coming, and when it does, so does the familiar ritual: sprinting across a car park doing the tip-toe dance because the pavement is frying the soles of your feet through a few millimetres of flat rubber...