Choosing the Best Insulation: Synthetic vs Down in Winter Coats

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Puffy jackets are a dime a dozen, but what’s inside is what really sets them apart. Sure, they all look similar – baffling, cinching, tear-resistant outer fabric – but it’s what’s inside that counts.

The best insulating equipment – whether a jacket or a sleeping bag – needs to be warm, light, and packable. Down and synthetic-filled products both offer these qualities, but there are pros and cons to each.

Natural down is lighter and warmer. It’s the fluffy stuff that comes from the layers under the protective exterior feathers of geese and ducks. It works for them while they float and fly around every winter, so of course, it keeps us warm too. But when natural down gets wet, it clumps and loses its heat-retaining ability. That’s where the outer shell of fabric comes in.

The warmth of down is measured by fill power, which is a numerical rating that usually ranges from around 450 to 900. This number comes from a standardized test where an ounce of down is compressed in a graduated cylinder and then measured for volume in cubic inches. The higher the fill power, the more warmth a jacket provides per ounce.

At the end of the day, down is an animal product. While big efforts have been made by brands like Patagonia and The North Face to source down ethically, not all down is sourced ethically, and animal cruelty can become part of the production chain.

Synthetic down, on the other hand, is our attempt to mimic natural down’s insulation power with polyester fibers arranged in different sizes that cluster and trap heat. It’s hypoallergenic and really does insulate well, without losing packability or lightness. The primary trade-off is that synthetic down weighs slightly more than natural down, so synthetic-filled gear tends to be marginally heavier and bulkier.

But synthetic down is less prone to clumping when it gets wet, so in mixed weather conditions, it might be a safer bet. It’s also worth noting that active insulation, a type of synthetic insulation, is incredibly breathable and designed for action.

Active insulation garments are insulating pieces meant to be worn during activity. By contrast, down (and traditional synthetic down) jackets are generally more appropriate for after you’ve started to cool down. Active insulation is the most breathable form of synthetic insulation available today, thanks to a construction that prevents the migration of fibers within the piece while allowing for extra stretch and superior moisture management.

Many active pieces are designed with an exterior shell that’s also more breathable but is often softer and less water-repellent than what’s found in other synthetic apparel. All active insulation, no matter the brand, is designed to prevent lots of layer swaps so that it can be worn throughout the entirety of an activity like hiking, climbing, or skiing.

So, how can you tell if your jacket is down? If a jacket just says “down,” it’s definitely natural. You might see fancy terms added in, like Mountain Hardwear’s proprietary Q.Shield waterproofing treatment. But if it’s “down,” it’s still the real deal. Synthetic insulation, on the other hand, goes by a lot of names, depending on the brands associated with it, but synthetic down insulation will never be labeled as “down” unless it’s a clearly labeled mixture of real and synthetic materials.

Ultimately, the decision comes down to preference. If you’re vegan or generally averse to using animal products, it’s an easy call. Otherwise, it’s a matter of price and use-case. Down is essential for cases where every ounce of weight counts, while synthetic is a good option for those who want a more affordable and breathable option.