Down vs Synthetic Insulation: Which Jacket Fill Is Right for You?

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Down is warmer for its weight, packs smaller and lasts longer. Synthetic insulation keeps more of its warmth when it gets wet, dries faster and costs less. Choose down for cold, dry conditions and packability; choose synthetic for damp climates, sweaty activity and easy care.

I have worked with fibers, fills and fabric finishes for 14+ years. Here is how the two insulations work and how to choose between them.

Down vs synthetic at a glance

	Down	Synthetic
What it is	Clusters from the undercoat of ducks or geese	Polyester fibers, as continuous sheets or loose clusters
Warmth for weight	Excellent	Good
Packability	Excellent	Fair to good
When wet	Clumps and loses much of its loft	Keeps much of its warmth
Drying time	Slow	Fast
Lifespan	Long; can last many years with care	Shorter; loses loft as fibers break down
Washing	Down wash, long low-heat drying	Easier; normal gentle cycle
Price	Higher	Lower

How insulation works

Neither fill makes heat. Both trap still air warmed by your body, and the more still air they hold for their weight, the warmer they are. Down clusters are three-dimensional puffs of fine filaments that spring apart and fill space. Synthetic fills copy that with fine, often hollow or crimped polyester fibers.

Fill power and fill weight

Fill power measures how much space one ounce of down fills: higher numbers mean more loft and more warmth for the weight. Fill weight is how much down the jacket contains. A 600-fill jacket stuffed with plenty of down can be warmer than an 800-fill jacket with a thin layer. Synthetic fills are usually rated in grams per square meter instead. Learn more in goose down vs duck down.

What happens when they get wet

Wet down clusters collapse and stick together, so the loft and most of the warmth disappear until they are dried. Polyester absorbs almost no water, so a synthetic fill keeps much of its structure when damp. Hydrophobic (water-resistant) down narrows this gap but does not close it.

Durability

Good down, cared for well, can keep its loft for many years. Synthetic fibers break down slowly each time they are compressed, so a synthetic jacket that lives in a stuff sack loses warmth faster. If you want one jacket for a decade, down is usually the better investment.

Ethics and sourcing

If animal welfare matters to you, look for down certified under the Responsible Down Standard (RDS) or a similar program, which audits the supply chain against live-plucking and force-feeding. Recycled down is another option. Synthetic fills avoid animal products altogether, and many now use recycled polyester.

Which should you choose?

Your situation	Better choice
Cold, dry winters	Down
Rain, sleet, wet snow, coastal cities	Synthetic, or down with a waterproof shell
Backpacking and travel	Down for packability
High-sweat activity (running, ski touring)	Synthetic
Tight budget	Synthetic
One jacket for many years	Down

Shopping for one? See the best down jackets for men, the best down jackets for women and the best packable down jackets. For care, read how to wash a down jacket.

Frequently asked questions

Is down warmer than synthetic insulation?

Yes, for the same weight. Down traps more air per ounce, so a down jacket is warmer than a synthetic one of the same weight.

Is synthetic insulation better in rain?

Yes. Synthetic fill keeps much of its warmth when damp, while down collapses when wet.

How long does a down jacket last?

With good care, many years. Down usually outlasts synthetic fill, which loses loft as its fibers break down.

What is hydrophobic down?

Down treated with a water-repellent finish so it resists moisture and dries faster. It helps in damp conditions but is not waterproof.