Down vs. Synthetic Insulation: What’s the Difference?

When it comes to down insulation, the technology can be a little confusing. Most people know that it has something to do with puffy feathers inside jackets and sleeping bags, but after that the details get hazy. A key question folks often have is, what’s the difference between natural down and synthetic insulation? To help you understand these distinctions a bit better, we've put together this easy guide below.

Natural down, sometimes called “real down,” is the stuff that comes from geese and ducks. Although it has a soft, fluffy texture that’s similar to feathers, it’s not exactly the same thing. Feathers are found on the outermost layer of a bird where you’re accustomed to seeing them, on their wings and backs. Down is the layer underneath the feathers, where its main purpose is to keep the birds warm.

Unlike regular feathers, which have long, poky quills in the middle, down is usually ultra-soft and fluffy with fibers that fan out in all directions. It’s also less dense and therefore more lightweight than feathers. When used as insulation for things like sleeping bags, pillows, or puffer jackets, it is typically formed into clusters and placed in panels of stitching known as baffling, which prevents it from clumping together or getting bunchy.

Synthetic down, also called alternative down, is a type of engineered insulation that’s aimed at mimicking natural down. It’s usually made with polyester and constructed so that the faux fibers branch out in different directions, offering varying sizes and shapes. Like natural down, it keeps you warm by trapping air next to your body and preventing heat from escaping. A key feature of synthetic down is its ability to maintain its insulating properties when wet. It comes in various types including Thermarator™, which has soft, extra-fine fibers and a high warmth-to-weight ratio.

In simple terms, fill power is the measure of how much space in cubic inches is produced by one ounce of down. The metric is sometimes referred to as the “warmth-to-weight ratio” because it has to do with the warmth of a jacket relative to its mass or “puffiness.” Although a higher fill power number doesn’t always mean the jacket is warmer, it does indicate that it’s more efficient for its size and weight. So if you're deciding how to pick out a puffer jacket, for example, fill power might be one of the metrics you would look at. Note, however, that it is only used to describe natural down and doesn't apply to synthetic insulation.

• Natural Down: One of the biggest pros of natural down is that it tends to be ultra-lightweight and extremely compact, offering exceptional warmth that isn’t heavy or bulky. This allows it to pack down easily, often compressing better than synthetic versions. It is also extraordinarily durable and tends to last for a long time. The downside to natural insulation is that it doesn’t perform as well when wet, often getting clumpy. It is also tougher to clean.
• Synthetic Down: The main advantage of synthetic down is how well it continues to keep you warm, even when wet. Additionally, it’s hypoallergenic and easy to clean, making it an overall low-maintenance product. What’s more, it dries quickly and doesn’t have poky feathers that can leak out when the exterior is damaged. That said, it is also heavier and bulkier than real down with a lower warmth-to-weight ratio.