Down Jacket Warmth

March 9, 2023

How should you compare the warmth between two different down jackets?

Since warmth and temperature ratings are subjective to both personal preferences and your overall layering system, it can be difficult to compare jackets head to head. It starts to feel like a convoluted high school math word problem: If Pemba’s jacket weighs nine ounces and has a fill power of 850, and Amity’s Jacket weighs 12 ounces and has a fill power of 700, who is warmer?

Let's break it down.

The two numbers that you should pay attention to when looking at a down jacket are: Fill Power and Fill Weight. To keep it simple, fill power is the quality of the down, and fill weight is the quantity of down. The warmest down items will have high quality down (a high Fill Power, 800+), and a lot of it (+3oz for a midweight down jacket, and +7oz for a Parka).

What are some other things to look for in a high quality down jacket?

1) Responsibly Sourced Down. Since down comes from either Ducks or Geese, it is important to choose down options that have been vetted by a 3rd party to ensure that these animals are treated humanely. The Responsible Down Standard works to ensure the highest possible standard that down and feathers don’t come from animals that have been subjected to unnecessary harm (you can learn more about them here). We use RDS certified down for all of our down products.

2) Waterproofing. The biggest pitfall of a down jacket is that once the plumes get wet, it is highly ineffective as an insulating layer. The plumes within will clump together and not loft up until they have fully dried (which may take a while). The solution? Look for a down jacket that has some type of waterproofing. For example, HIMALI uses HyperDRY™ Fluorocarbon Free water resistant down in all of our down jackets to protect against unwanted moisture. While this does not make your down jacket waterproof, it will help delay decreases of insulation due to moisture.

3) Weight. Down as insulation is a great option when looking for lightweight gear that is built to last. When choosing a down jacket, you should consider both the overall weight of the jacket and the fill weight of the jacket. This will help you to determine how much of the weight of the jacket is from the insulation (down) vs everything else (fabric, zippers, etc). Ultralight enthusiasts may want to go with the lightest jacket on the market, but you also might want to consider if other features are important to you (durability, pockets, etc) to make the best choice for you.

What is Fill Power?

Down Fill power is arguably one of the most important factors to consider when buying down gear, but it can be a difficult concept to understand. In short, fill power is a measure of the quality of down. The higher the fill power, the higher the quality of the down, the warmer the down is (per ounce), and the more expensive it is to purchase.

If you want to get specific, fill power measures the volume one ounce of down will fill when allowed to fully loft. So, one ounce of 700 Fill Power Down will fill a space of 700cm3, and one ounce of 850 Fill Power Down will fill a space of 850cm3.

Why is this important? Down keeps you warm by trapping air between the individual plumes. As you wear the jacket, you heat up the air between the plumes & the down holds it close to your body. Higher fill power down creates more of these air pockets for your body to heat up & keep close, making for a warmer jacket (per ounce).

disclaimer: While higher fill power does translate to greater loft and insulating potential, it is important to remember that the warmth of a piece of gear/temperature rating is a subjective measure. There are many factors that affect the warmth of down, including activity level, how many ounces of filling are in the gear, personal metabolism, etc.