Buyers' Guide - Insulated Clothing

It helps if you understand how insulation works - basically what keeps you warm isn't the fabric or the filling, but the air which is trapped inside it and warmed by your body. The more air you can trap, the warmer the insulating garment will be, everything else being equal.

That's why different grades of down give different levels of insulation depending on how much space they expand to occupy, which is why fill-power ratings are important. Synthetics don't trap as much air, so generally pound for pound aren't as warm as down, but they have other advantages.

Finally, it's essential that any insulated garment has a windproof outer shell. Without it, any wind will simply strip away the warm air trapped inside the insulation and leave you chilling as your body re-warms the air again and again.

Top tip Damp air transmits heat faster, so an insulated jacket that's comfortable at -20 in Nepal may feel chilly at -10 in damp old Scotland.

Unless it's seriously cold, and we mean well below freezing point, only thin insulated garments will be any use at all for active use. When you stop moving however, it's a different matter. You'll cool fast and a big, fat insulated jacket is ideal for keeping you comfortable in winter conditions. Of course it's ideal for that snowy walk to the pub too, but we wouldn't do that, erm, would we?

The logical extension of the layer-up when stopped principle is the 'belay jacket', a system developed by winter climbers. While actually climbing and working hard they wear thin, breathable layers. But at the end of a pitch and on belay, they simply throw on an over-sized insulated jacket over anything else they're wearing.

Once they move off and are climbing again, the process is reversed. It works really well and not just for climbers. There's no reason why walkers and mountain bikers can't do the same.

Top tip most people wear too much when moving, but not enough when stopped still and cooling down.

Goose and duck down is fantastic stuff with an amazing warmth to weight ratio and a small pack size, it has one major disadvantage though. If down gets damp then the surface tension of the water overcomes the ability of the lighweight fluff to loft up and the whole thing collapses into a porridgy mess that offers no insulation at all.

That means that while down is great in cold, dry, high mountain environments like, say, the Alps or the Himalaya, in damper conditions like the UK, you have to be very careful to keep it dry, which is sometimes easier said than done.

Down is also fussy to care for, you need to either have it professionally cleaned or use special cleaning products yourself and washing tends to degrade its performance slightly every time.

You'll see fill-power figures quoted for down, they are based on the volume of space that a certain weight of the down will occupy, so the higher the number, the warmer the down. So 600+ down is slightly less warm for a given weight than 700+ fill power down, in which case you can use the same amount of the higher rated down and get a warmer garment or use less of it for the same warmth.

Generally manufacturers won't quote temperature ratings as so much depends on other factors, like the humidity, what is worn underneath the insulation and individual physiology, but full-weight down duvet jackets are generally too warm for active use unless it's ridiculously cold, ie well below zero.

Top tip The best down tends to be eastern European goose down.

Synthetic insulation - the best known is Primaloft, but there are plenty of alternatives - tends not to be as warm for its weight as down, but has far more of a knockabout character. It still retains a reasonable proportion of its insulating abilities when wet and can be washed using normal detergents without problems.

That makes it a great choice for damp, cold places like, well, the UK really and is an ideal filling for a British throw-over belay jacket which may have to cover damp clothing.

The gap between down and synthetics is closing as well with hollow fibres and soft feel making some synthetics feel almost luxurious these days.

Top tip Primaloft One is the closest synthetic insulation to down in terms of softness and weight for warmth ratio, but is more water friendly.

Starting with down, ideally you want a windproof outer fabric with some sort of water-repellant treatment. Waterproof down tops are really pub coats, you shouldn't be wearing down in conditions where it's warm enough to rain anyway...

There are two basic forms of down construction: box wall - [] - which puts the down in a walled-channel which, in turn, eliminates cold spots and the simpler 'sewn-through' construction where the inner and outer materials are simply sewn together to create a channel - () - creating cold spots where the stitching is.

Sewn-through is light and simple, but down garments designed for extreme conditions generally use box-walls because of the increased warmth and lack of cold spots.

Look for insulated zip baffles on both synthetic and down jackets to prevent zips becoming cold spots. Handwarmer pockets are great too and, well, give you somewhere to put your hands when it's cold. Adjustable cuffs seal the wrist opening and minimise heat loss there, ditto collars. An insulated hood, possibly a detachable one, is an ideal way of keeping your head warm with minimal fuss. You also want a close-fitting hem, again to prevent heat loss from down below.

A water-resistant outer shell fabric will deal with snow and contact with damp surfaces, but won't stand up to heavy rain; then again, you shouldn't be wearing down in heavy rain.

Most of the above principles also hold true for synthetics, though construction may be different with batts of synthetic fabric being glued or stitched in place.

Top tip A good feel is the easiest way to distinguish between box and sewn-through construction; try pulling the inner and outer stitching apart and you can feel the difference.

More of an alternative to fleece than a step-up, lightweight insulated garments score by packing smaller and offering windproofing in addition to warmth. The choice between down and synthetics is down to the same factors as with heavier jackets and, again, synthetics are arguably more versatile for UK conditions, with lighter, warmer but more expensive down scoring in cold, dry, high mountain environments.

They don't have the same 'pub snug' appeal as fleece, but are more effective in performance terms and generally warmer for the weight as well.

Top tip Buy loose and you can use a lightweight synthetic garment like a belay parka and simply pull it over the top of everything else when you grind to a halt.

More Help and Advice

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