The world of outdoor gear is full of exciting technical terms, jargon, and numbers that can be tricky to grasp if you’re new to it. Choosing insulation involves options like down versus synthetic materials, warmth-to-weight ratio, and fill powers, which may seem overwhelming at first glance. Fear not, my fellow outdoors people; once you get the hang of it, you’ll feel like a pro when picking the perfect insulation for your next adventure. Let’s break down the key factors of down and synthetic insulation for clothing so you can pick the right garments to stay warm and comfortable on your adventures.
Loft
Think of loft as the “puff factor”—little air pockets that trap heat within clusters of down feathers or synthetic fibers. For example, when you compress a sleeping bag, you squeeze out the air, which reduces its loft. This is why it’s important to keep your insulated gear from getting compressed, whether from packing, getting wet, or simply being worn out, as it loses its ability to trap heat. The higher the loft, the better a garment traps body heat.
At first glance, you might assume a jacket’s warmth is obvious; puffier means warmer, right? However, this isn’t always the case. While you can generally gauge a coat’s warmth by its volume (i.e., the amount of down or synthetic fibers), true warmth depends on fill power or fill weight.
Fill Power, Fill Weight, and Warmth-to-Weight Ratio
Fill power and fill weight are two distinct measurements that determine an insulation’s warmth (fill power does not equal fill weight). Although down jackets can be measured by either fill power or fill weight, the industry generally highlights fill power because brands market it more frequently, and consumers recognize it more easily. Synthetic insulation, on the other hand, uses a straightforward grams per square meter (g/m²) measurement to calculate warmth.
Fill Power
Rather than a measure of how much down is in a garment, fill power indicates how much loft the down holds. A higher fill power garment will generate more loft with less weight and volume. In a sense, it measures the quality and efficiency of the down insulation. And remember, the higher the loft, the more air it traps. More technically, the fill power number is calculated by how many cubic inches an ounce of down creates. An 800-down jacket means one ounce of down can cover 800 cubic inches. Fill power in outdoor jackets range anywhere from 400 on the low end to 1,000 on the high end.
Higher fill power = More efficient, lofty insulation
Fill Weight
Fill weight, then, tells you the weight of the amount of down feathers or synthetic filament within a garment. You will find this measured in either ounces (oz.) or grams (g). For example, a vest with a 3 oz. (85 g) fill weight contains 3 ounces of filament. The reason you should pay attention to fill weight becomes clearer when you look at two jackets with the same fill power; the one with a higher fill weight will deliver more heat because it uses more down.
Higher fill weight = More insulation
Hopefully, this makes the concept clear, but let’s combine these ideas and put them into practice. You can increase either fill power or fill weight to improve a jacket’s warmth. A higher fill power means the down lofts more efficiently, creating a lighter, more packable jacket. In contrast, a jacket with lower fill power won’t loft as well, requiring more down to trap the same amount of air.
Below, you’ll notice both Norrona Jackets carry the same fill power, marked as 800 FP on the tag. However, the piece on the left has a higher fill weight, making it heavier, bulkier, and ultimately warmer.
Warmth-to-Weight Ratio
This is where the warmth-to-weight ratio comes into play. Simply put, the efficiency of the insulation—whether down feather or synthetic fibers—directly affects the weight and space required to produce the same level of warmth.
Higher warmth-to-weight ratio = Less weight for the same warmth
As an example, let’s compare the Norrona Trollveggen Down800 Hooded Jacket to the Arcteryx Cerium SV Hoody (shown below). Both down insulation jackets provide exceptional warmth for the same types of severe cold-weather adventures.
You might glance at each from a distance in a store and assume Norrona’s Trollveggan Down800 jacket is warmer because it is clearly puffier. However, Arcteryx’s Cerium SV Hoody has 1,000 fill power grey goose down, while the Trollveggen has an 800 fill power 90/10 mix of down to feathers. The Cerium SV’s higher fill power creates more loft and requires less down to trap similar amounts of heat (greater warmth-to-weight ratio). Conversely, the Trollveggen uses a higher fill weight to achieve the same warmth as the Cerium SV, hence the puffier profile.
Down vs. Synthetic (eco-friendly, hydrophobic & PFAS)
When it comes to insulation, both down and synthetic fills have their strengths. For maximum heat retention, down remains the gold standard. Down comes from the soft undercoat of ducks or geese and naturally has a lofty structure that allows it to trap heat. Garments made with down can compresses to a much smaller size, making them convenient for packing. Down does have a major weakness—it absorbs water, clumps together, and loses its insulating properties when wet.
Synthetics step up where down falls short. Synthetic insulation mimics down’s loft and heat-trapping ability. But, unlike down, synthetic fill is hydrophobic, meaning it won’t compress and lose its loft when it gets wet.
Outdoor brands have developed solutions to make down more water resistant. Hydrophobic down undergoes a water-repellent treatment, allowing it to withstand moisture better than untreated down while retaining more loft and insulating power when wet. Additionally, many down jackets feature a Durable Water-Resistant (DWR) finish or a waterproof membrane to protect against the elements. However, these treatments often contain PFAS (commonly known as “forever chemicals”) that raise environmental concerns. For outdoor enthusiasts, sustainability is key to preserving the beauty we enjoy and choosing PFAS-free gear supports this goal.
Despite these advancements, down still falls short in prolonged wet conditions or heavy downpours. In contrast, synthetic insulation continues to perform, making it the better choice for damp environments. Ultimately, the right insulation depends on the demands of your specific adventure. If you need a packable garment and superior warmth, then down is the way to go. If you’re expecting wet weather, then synthetic insulation is the smarter pick.
Body-Mapped Insulation
One unique technique gaining popularity in the outdoor industry is body-mapped insulation. Outdoor companies are using this approach to maximize warmth while enhancing key performance factors like mobility and moisture control. You might notice more compact insulation in the arms for better movement, while the core features extra fill for optimal heat retention. Brands also strategically mix natural down with synthetic insulation in different areas of a garment to get the most out of each fill’s advantages, namely high warmth-to-weight ratio and hydrophobic capabilities.
The Arc’teryx Cerium SV Hoody mentioned above is a great example of body-mapped insulation. Lofty goose down is used for the core to retain heat, while synthetic PrimaLoft insulation is used in the underarms to help manage sweat.
Baffle Styles Make a Difference
When it comes to down jackets, two primary construction methods—box-baffling and sewn-through baffling—are used, each bringing its own strengths to the table.
Box-baffling features small “boxes”, or pockets, of down between the inner and outer layers of the jacket. This construction allows the down to loft more, trapping more air, which results in greater warmth. It also reduces cold spots where baffles meet at the stitching. Box baffling offers more effective insulation, but it requires more time and effort to produce and is more expensive.
Sewn-through baffling, on the other hand, is a more common, straightforward, and cost-effective method. The outer material is stitched directly into the inner lining, dividing the down into separate baffles, usually horizontal or rectangular. While this method is easier and costs less to manufacture, it compresses the down at the seam, creating gaps in the insulation or “cold spots”.
Choosing the Right Insulation for the Mission
Choosing the right insulation boils down to balancing your needs for warmth, weight, and moisture resistance. If you’re planning on extreme cold conditions where wet weather is less of a concern, then down with high fill power offers unmatched warmth. Down is the top choice for long-lasting warmth in dry conditions, delivering exceptional heat retention and compressibility. However, if you’re expecting damp environments or unpredictable weather, synthetic insulation provides reliable warmth, even when wet, and it dries quickly. Need versatility? A body-mapped garment may be your best solution.
Always consider your activity, climate, and packing needs. When it comes to insulation, there’s no one-size-fits-all. Focus on weather conditions, fill power, and fill weight to select the right insulation for your adventure.
By Broc Helgeson, Content Writer, jans.com
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