You Don’t Need a Heavy Winter Coat for Cold Weather

Winter Coat Insulation: Down vs Synthetic

Down Insulation 

Down comes from the soft feathers of birds, like ducks or geese, and traps heat really well without adding bulk.

Pros:

• Warmth-to-weight: Lightweight yet super warm, perfect for packing without bulk.
• Durability: High-quality down lasts years and bounces back after storage.

Cons:

• Ineffective when wet: Clumps, loses fluff, and stops insulating if soaked.
• Allergy risk: May trigger feather or dust mite allergies.

Some manufacturers now treat down feathers with DWR coatings, which helps, but they’re still not as water-resistant as synthetic insulation.

Synthetic Insulation 

Synthetic insulation is made from materials like polyester and is designed to mimic the way down works by trapping air to hold in heat. 

Pros:

• Performs when wet: Stays warm and fluffy even in rain or snow.
• Allergy-friendly: Self-explanatory.
• Tougher: Handles rough use and wear better than down.

Cons:

• Heavier: Bulkier and heavier than down for the same warmth.
• Less packable: Doesn’t compress as easily for storage or travel.

Brands like PrimaLoft, Polartec Alpha, and G-Loft have created some incredible synthetic options that come pretty close to mimicking the warmth and feel of down.

Down Jackets: Fill Power and Fill Weight

When comparing down jackets, two terms you’ll see a lot are fill power and fill weight.

What is Fill Power?

Here’s where it gets slightly technical but don’t worry, it’s easy to understand. Fill power (sometimes shortened to FP) measures the “fluffiness” of the down. It’s basically a number that tells you how much space 1 ounce of down can fill. 

For example:

• 700FP means 1 ounce of down fills 700 cubic inches of space. 
• 850FP means 1 ounce of down fills 850 cubic inches. 

The higher the fill power, the better the down is at trapping air—and the warmer it is. Higher fill power = more warmth with less down (so the jacket is also usually lighter). 

Pro Tip: If you’re looking for something ultra-light and for extreme cold, go for a jacket with higher fill power.

What is Fill Weight? 

Fill weight is just as important as fill power, but it gets overlooked. While fill power tells you how efficient the down is, fill weight tells you how much down is actually in the jacket. 

Think of it this way:

• Fill power = quality of the down. 
• Fill weight = quantity of the down. 

For example, you could have two jackets with 700FP down, but one might have 5 ounces of down and the other might have 8 ounces. Which one will keep you warmer? The jacket with 8 ounces of down—because there’s simply more insulation inside it.

When shopping, look for both fill weight and fill power together.

How to Read Fill Power and Fill Weight Together 

Here’s a quick cheat sheet to help you spot the difference:

• Low fill power (500-650): Decent warmth, but often requires heavier down to keep you cozy. Best for milder winters or casual everyday wear. 
• Mid-range fill power (700-800): Great balance of warmth, weight, and packability. These jackets are a solid choice for winter hikes, camping, or city wear in colder climates. 
• High fill power (850+): Top-tier insulation—lightweight but incredibly warm. Ideal for extreme cold or anyone who wants a performance-oriented jacket. If you need to shove your jacket into a small bag for traveling, look for something in the 800-900FP range.

Fill Weight in Action 

Imagine two jackets side by side:

1. Jacket A: 700FP, 10 ounces of down. 
2. Jacket B: 850FP, 6 ounces of down. 

Which one’s warmer? Surprisingly, Jacket A is likely to feel warmer in most cases because it has more down packed inside it (10 ounces vs. 6 ounces). But Jacket B is lighter and more compressible while still offering excellent warmth—it just depends on your priorities.