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We explore the benefits and drawbacks of two of the most popular types of insulation available today.

A puffy jacket is a puffy jacket, right? It's not quite that simple. Puffy jackets certainly follow a familiar design archetype — baffling, cinching, tear-resistant outer fabric — but it's what inside that truly differentiates one jacket from another. If you've ever been curious what differentiates down from synthetic imitations, and which is best for you, look no further.

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

Down comes from the layers under 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 as well. But when natural down gets wet, it clumps and loses a lot of its heat-retaining ability. In nature, exterior feathers keep it dry. In your coat, it's an outer shell of fabric.

The warmth of down is indicated by fill power: numerical ratings that usually range anywhere from about 450 to 900. This number comes from a standardized test in which an ounce of down is compressed in a graduated cylinder and then measured for volume in cubic inches. That volume is the fill rating.

Down has the most warmth for the weight, but performs poorly when wet.

Bottom line: The higher the fill power, the more warmth a jacket provides per ounce of weight. In terms of weight-to-warmth ratio, down usually beats synthetic, and in extremely cold environments (which are often dry) down protects and insulates better than its synthetic counterpart.

At the end of the day, down is an animal product. And although big efforts have been made by a lot of brands and outfitters such as Patagonia and The North Face, not all down is sourced ethically, and animal cruelty can become part of natural down insulation’s production chain.

Synthetic insulation is our attempt to mimic natural down’s insulation power with polyester fibers arranged in different sizes that cluster and trap heat much like the real thing.

Synthetic fillings are heavier than down, but only marginally.

Synthetic down really does insulate well, without losing packability or the lightness of natural down — not to mention it’s hypoallergenic. 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.

On the flip side of the coin, synthetic down is less prone to clumping when it gets wet, so in mixed weather conditions, it might be a safer bet.

Technically, active insulation is a type of synthetic insulation (a water-resistant alternative to down), but because of some fundamental differences that make it unique, active should be considered on its own. Active insulation garments are insulating pieces that are 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.

What makes active insulation better for action? It's incredibly breathable. How this is achieved depends on the specific insulation used in the jacket, and every company uses a different version. Some are proprietary, like Patagonia’s FullRange insulation, and some, such as Polartec’s Alpha insulation, which was originally developed for the US Special Forces, are sourced by a range of companies.

As with other types of synthetic insulation, active insulation is highly water-resistant and compressible. In comparison to regular synthetic insulation, active 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.

In terms of labeling, if a jacket just says “down” it’s definitely natural down insulation. 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. You should also know that although the industry is still improving and innovating ways to make down more water-resistant, no feathers are truly waterproof.

Synthetic insulation 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.

A lot of 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. There's simply no beating down when it comes to high intensity backpacking or mountaineering. If you're going to be in extremely cold environments and want the strongest warmth-to-weight ratio a jacket can provide, down is going to be your best bet.

But if price is a primary concern, and a little extra weight is a non-issue, synthetic will get you much more bang for your buck, and keep you plenty warm while you're out walking the dog.