Down vs Synthetic Insulation

When you're choosing an insulated jacket or sleeping bag, one of the big decisions is down or synthetic insulation.

Neither is simply better than the other. Down generally wins on weight and packability, while synthetic insulation is usually the safer bet when damp or wet conditions are likely.

Down is the soft, fluffy plumage found underneath the outer feathers of ducks and geese. Its loft traps air, creating a very effective layer of insulation.

Its biggest advantage is its warmth-to-weight ratio. A good down jacket or sleeping bag can provide plenty of warmth while remaining remarkably light, and it can compress into a very small space. With proper care, quality down can also retain its loft for many years.

The downside is moisture. When down becomes properly wet, it clumps together and loses much of the loft that keeps you warm. It can also take a while to dry.

Many modern products use hydrophobic or water-resistant down, which helps it cope with moisture better than untreated down, but it still isn't something you want to get soaked.

Down is a great choice if:

• Keeping weight down matters.

• You need your gear to pack up small.

• You're expecting mostly cold, dry conditions.

• You're happy to take a little extra care to keep your gear dry.

You'll often see down described as 600, 700, 800 or 900 fill power (or FP).

Fill power is a measure of how much space a given amount of down occupies when fully lofted. Higher-quality down lofts more effectively, trapping more insulating air for its weight.

So, for example, 800-fill down isn't necessarily warmer than 650-fill down. A jacket containing lots of 650-fill down could be warmer than a very lightweight 800-fill jacket.

What the higher number tells you is that the down is more efficient for its weight. This allows manufacturers to make warm gear that's lighter and more compressible.

Synthetic insulation is usually made from polyester fibres designed to trap warm air in much the same way as down.

Its big advantage is that it continues to provide useful insulation when damp or wet, and it generally dries much faster than down. It's also usually cheaper.

The trade-off is weight and bulk. For roughly comparable warmth, synthetic insulation will generally be heavier and less compressible than down. It can also gradually lose some of its loft after repeated compression and use.

Synthetic is a great choice if:

• You're expecting wet, damp or humid conditions.

• Your gear is likely to get wet during use.

• Weight and packed size aren't your highest priorities.

• You want a more affordable option.

• You want something that's generally straightforward to look after.

For an insulated jacket, think about how you're going to use it.

A lightweight down jacket is hard to beat as a warm layer you can carry in your pack and pull on when you stop. You get lots of warmth without carrying much weight or taking up much pack space.

Synthetic jackets can make more sense when you're likely to be wearing the jacket while you're active, particularly in damp weather. Moisture doesn't only come from rain — sweat can also make insulation damp from the inside.

For changeable, wet conditions, synthetic insulation therefore gives you a bit more margin for error.

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The same basic trade-offs apply to sleeping bags, but weight and packed size become particularly noticeable when you're carrying everything on your back.

For tramping, fastpacking or other trips where every gram and litre of pack space counts, down is very appealing. A down bag can provide excellent warmth while packing considerably smaller than an equivalent synthetic bag.

Synthetic sleeping bags are often a good option when you're expecting damp conditions, aren't travelling particularly light, or simply don't need to pay extra to save weight and pack space.

For car camping, for example, there's often little advantage in paying considerably more for an ultralight down bag if you're not actually carrying it very far.

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There's no universal winner.

Choose down when low weight, warmth and a small packed size are priorities and you're confident you can keep it reasonably dry.

Choose synthetic when wet or damp conditions are more likely, when your gear may regularly get sweaty, or when price matters more than shaving grams and pack volume.

And remember that the insulation is only part of the story. The amount of insulation, construction, outer fabrics and overall design all affect how warm a jacket or sleeping bag actually is.

For sleeping bags in particular, use the bag's temperature rating to compare warmth rather than assuming that down automatically means warmer than synthetic.