What you’ll need

▶ Two small reusable hand warmers – the ones we used measured 9cm x 5.5cm. These can be purchased from many sources online.

▶ A thermal sock that’s wide enough to hold the hand warmers and long enough to fit around your camera lenses.

▶ A sewing machine (optional), needle and thread. Two buttons (we used ones that were 2.2cm in diameter), and two pieces of elastic, about 4cm long; we used 0.5cm-wide elastic, but any pieces will do.

▶ Two strips of Velcro; we used 5cm of loops and 11cm of hooks. This allows you to fit the dew heater around different sized lenses. (If you don’t have any Velcro you can thread shoelaces into small holes at each end, then tie them together to secure the dew heater in place.)