PREVENTING HEAT LOSS

Outdoor clothing has been developed to combat all types of heat loss, but it mostly focuses on insulating against

convection. The best insulator we have is air itself, so systems like feathers, down and wool all work by creating a ‘ loft’, or depth, which traps a layer of air near your skin. Artificial lofting textiles like Polartec, Alpha or Primaloft mimic this effect without animal products.

But loft only works as an insulator if there’s no air-flow through the fabric to take the warm air away. On a breezy day your outer layer must also stop as much of the wind as possible from whipping through your fabrics. That’s why an insulated jacket has a shiny outer face – that’s a tightly-woven windproof fabric which tries to prevent the cold air getting to the loft layer.

But remember that stopping breezes is as much a function of elasticated hems, cuffs, zipper baffles and a good, close fit – so trying garments on for size is a must when it comes to winter kit.

Insulating against the other types of heat loss is more of a specialist affair. I have a pair of Páramo mountain salopettes with a foam panel sewn in to the backside so I can sit down and not get a cold posterior. It’s a complex way to beat conduction, but it works.

And some brands have experimented with preventing radiant heat loss. Columbia’s Omni-Heat range uses reflective silver dots to bounce back your heat like one of those emergency silver blankets you see after marathons and in rescue dramas. Radiant heat only represents a small amount of heat loss compared to the other methods though, so it’s usually coupled with traditional lofting fabrics as well.