How to Choose an Insulated Jacket
An insulated jacket keeps you warm by trapping body heat using either down or synthetic fill.
Down insulation is natural, lightweight, and highly packable. Its warmth depends on:
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Down ratio – the percentage of down vs. feathers (e.g., 90:10 offers more warmth than 80:20).
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Fill power (FP) – measures loft and insulation efficiency. Higher FP (800–1000) gives more warmth for less weight but can be less durable. Lower FP (700–750) is tougher and better in harsher conditions.
Down works best in cold, dry climates. It performs poorly when wet, though some jackets use water-resistant down or waterproof shells to offset this. Down jackets need careful washing and drying to maintain loft.
Synthetic insulation uses polyester fibres—often recycled—to mimic down. It’s warmer when wet, dries faster, and is easier to wash, making it ideal for cold, damp environments like the UK. It’s slightly heavier and less packable but more weather-resistant.
Choosing your jacket:
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Environment: Down for cold, dry; synthetic for cold, wet.
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Activity: Heavy down for static use (e.g., skiing, belaying); light synthetic for active use (e.g., hiking, running).
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Weight & packability: High FP down or loose-fill synthetic are best.
No single jacket does it all—pair midweight insulation with layers for versatility.