Down vs Synthetic
Walk into OD's and you'll find two kinds of insulated jacket sitting side by side. One is filled with natural duck or goose down. The other is filled with synthetic fibres. Both will keep you warm — but they do it differently, and they suit different people, different activities, and different weather conditions.
This guide explains how both types of insulation work, what fill power means, which brands at OD's use each technology, and how to choose the right jacket for you.
1 | How Insulation Works
Insulation doesn't generate heat — your body does that. What insulation does is trap the warm air your body produces and hold it next to you, forming a thermal barrier between you and the cold outside air. The more air a jacket traps relative to its weight, the warmer it feels.
Both down and synthetic insulation achieve this by creating thousands of tiny air pockets within the jacket fill. The difference is in how those pockets are created, how long they last, and how they perform when conditions change.
The Core Principle
- Insulation traps warm air — it does not generate heat
- More trapped air = more warmth
- Loft (the thickness and fluffiness of fill) determines how much air is trapped
- Both down and synthetic lose insulating ability when compressed or wet — to different degrees
2 | Down — The Natural Choice
Down is the soft underlayer of feathers found beneath the outer plumage of ducks and geese. Each individual down cluster is a three-dimensional structure that traps enormous amounts of air relative to its weight. It is the most efficient natural insulator ever found.
The Strengths of Down
Best Warmth-to-Weight
Down provides more warmth per gram than any synthetic alternative. A 600-fill-power down jacket weighs significantly less than a synthetic jacket of equivalent warmth.
Exceptional Compressibility
Down packs down to a fraction of its filled size and springs back to full loft when unpacked. Perfect for travel and layering under a shell jacket.
Long Lifespan
A well-cared-for down jacket can last 10–20 years. The natural clusters do not degrade the way synthetic fibres do over repeated washing and use.
Breathability
Down breathes naturally. It does not create a plastic-like heat trap the way some synthetic fills can during high-output activity.
The One Big Weakness: Wet Performance
Down Loses Its Loft When Wet
When down gets wet — from rain, snow, or heavy sweat — the clusters clump together, loft collapses, and warmth drops dramatically. A soaked down jacket can feel barely warmer than a thin fleece. Treated down (hydrophobic down) delays this problem but does not fully solve it.
This is the single most important factor in choosing between down and synthetic. If your activity or climate involves sustained wet weather, down needs careful thought.
3 | Synthetic — The Practical Choice
Synthetic insulation uses man-made polyester fibres — either continuous filament or short-staple — engineered to mimic the loft and warmth of down. Modern synthetic fills have closed the gap with down significantly, and in some conditions they outperform it.
Works When Wet
Synthetic fibres do not absorb water the way down clusters do. Wet synthetic insulation retains approximately 60–70% of its warmth — making it far safer in prolonged rain or high-sweat activity.
Lower Cost
Synthetic fills are less expensive to produce than ethically sourced, high-fill-power goose down. This makes synthetic jackets more accessible across price points.
Easier to Care For
Synthetic jackets can generally be machine washed without the same care and attention required for down. They are more forgiving of rough handling.
Heavier and Bulkier
The main trade-off. To match the warmth of a 700-fill-power down jacket, a synthetic jacket needs more fill, which adds weight and bulk. It also compresses less tightly for packing.
Synthetic is not the "inferior" option — it is the appropriate option for wet climates, water sports, skiing in heavy snowfall, or anyone who cannot be bothered with the care requirements of down.
4 | Fill Power Explained
Fill power is the measurement used to describe the quality and loft of down. It tells you how many cubic inches one ounce of down occupies when fully expanded. Higher fill power = more air trapped per ounce = more warmth for less weight.
Fill Power Scale at a Glance
- 600 fill power — Good quality. Solid warmth, accessible price. Most entry-level premium jackets.
- 650–700 fill power — Very good. Excellent warmth-to-weight ratio. Mid-tier premium market.
- 750–800 fill power — Outstanding. Expedition-grade warmth with minimal weight. High-end performance jackets.
- 850–900 fill power — Elite. The highest grade of goose down available. Parajumpers territory.
Fill Power Is Not the Only Factor
Fill power tells you the quality of the down, not how warm the jacket is overall. The amount of down used (fill weight) matters just as much. A jacket with 800-fill-power down but only a small amount of it may be less warm than a jacket with 650-fill-power down used generously throughout. Always consider fill power and fill weight together.
A Practical Guide
For mild British winters and urban wear: 600–650 fill power is more than sufficient. For Scottish Highlands, ski trips, or genuinely cold expeditions: 750+ fill power or a high-quality synthetic designed for extreme cold.
5 | Which OD's Brands Use Which Insulation?
At OD's Designer Clothing we stock a carefully chosen range of insulated outerwear. Here is how the brands break down by insulation type.
Down Insulation Brands
Parajumpers
Parajumpers is the benchmark for premium down outerwear. Their jackets use 800–900 fill power RDS-certified goose down — expedition-grade insulation in an urban silhouette. Built for extreme cold without the bulk.
The North Face
TNF uses both down and synthetic depending on the model. Their down range — including the 700-fill Nuptse — is among the most iconic performance down in the world. TNF's down is RDS certified.
Synthetic Insulation Brands
UBR (Uber)
UBR is a Finnish brand that builds jackets for Scandinavian winters. Their insulation is synthetic — specifically chosen for performance in persistently wet Nordic conditions where down's wet-weather weakness is a real problem.
The North Face (Synthetic Range)
TNF's ThermoBall and Heatseeker Eco lines use synthetic insulation. ThermoBall in particular mimics down clustering to deliver excellent packability alongside wet-weather resilience.
Browse Insulated Outerwear at OD's
6 | Best Insulation for Different Activities
Urban Winter Wear
Down wins. Walking to the office, shopping, weekend city breaks. You are not getting soaked. Down's superior warmth-to-weight and packability make it the smarter choice for everyday urban life.
Hiking & Trail Walking
Synthetic wins. Sustained output means sweat, and British weather means rain. Synthetic holds its warmth through both. Use as a mid-layer under a waterproof shell for maximum flexibility.
Skiing & Winter Sports
Synthetic or treated down. On-piste: dry powder favours down. Off-piste or in wet alpine conditions: synthetic or hydrophobic-treated down is safer. TNF ThermoBall is purpose-built for this.
Travel & Packability
Down wins. Down compresses into a stuff sack the size of a water bottle. A synthetic jacket of equivalent warmth will not compress nearly as small — relevant if you are packing light.
Dog Walking & Everyday British Life
Synthetic wins. Drizzle, muddy dogs, unpredictable showers. Synthetic insulation forgives the conditions that British daily life reliably delivers.
Extreme Cold — Expeditions
High fill-power down wins. In genuinely dry, extreme cold — think Arctic, high altitude — 850+ fill-power down (Parajumpers) provides warmth that no synthetic can match at a comparable weight.
7 | Frequently Asked Questions
Is down or synthetic insulation warmer?
In dry conditions, high-fill-power down (700+) is warmer than synthetic at equivalent weight. Synthetic insulation narrows the gap significantly when wet, and some synthetic fills are engineered specifically for cold-weather performance. For most people in the UK, the real question is not which is warmer in a lab — it is which performs better in the conditions you actually face.
What does 800 fill power mean?
Fill power measures how many cubic inches one ounce of down occupies when fully lofted. 800 fill power means one ounce of this down expands to fill 800 cubic inches of space. The higher the number, the more air is trapped per ounce — meaning more warmth for less weight. Parajumpers jackets at OD's use 800–900 fill power down, which is among the highest quality available.
Can you wash a down jacket at home?
Yes, but carefully. Use a front-loading machine (not top-loading with an agitator), a gentle cycle, cold or warm water, and a specialist down detergent. Crucially, dry fully in a tumble dryer on low heat with two or three clean tennis balls to break up clumped clusters — incomplete drying causes mildew and permanent damage to the down. Check the care label on your specific jacket before washing.
Is Parajumpers down ethically sourced?
Parajumpers uses Responsible Down Standard (RDS) certified down across their range. RDS certification means the down has been independently verified to come from birds that have not been live-plucked or force-fed. The North Face also uses RDS-certified down in their down jacket range.
How long does a down jacket last compared to synthetic?
A well-cared-for down jacket can last 10–20 years. Down clusters are resilient and recover their loft wash after wash when correctly cared for. Synthetic insulation typically degrades faster — fibres break down over repeated washing and compression, and most synthetic jackets show meaningful performance decline after 5–8 years of regular use. For a long-term investment, down holds its performance longer.