Fill Power & Fill Weight: Everything you need to know about Down Jackets 1

TLDR…

• Fill Power measures how fluffy the Down is. Higher FP traps more warm air.
• FP’s unit is CUbic INches of space occupied by one ounce of Down. Companies may just use CUIN instead.
• Fill Weight is the amount of fill, multiplying it with FP gives a vague idea of the warmth of the jacket.
• FP of a Jacket is found online, sometimes on material tag, and usually on the sleeve.
  

Fill Power (FP) is essentially the quality of down.

The higher the FP the warmer the jacket will be , assuming the jackets are of the same weight.(more on that later)

But what does it actually mean? How are those numbers made up? Where can I find the FP of a jacket?

This post will tell you all that.

It is not obvious which is warmer just by looking at them…

Down Anatomy: How fluffiness is measured

First of all we need to know a bit of Down anatomy.

The longer the filament, the more space one cluster of down will occupy. Which means it can trap more (warm) air.

Someone from America wanted to measure how much space a batch of down would occupy

They took 1 ounce of down and put it in a box/cylinder to see how much volume it takes up, measured in Cubic Inches (CUIN).

But CUIN doesnt sound intuitive enough, so people later started to call it Fill Power, although some companies still use CUIN.

For Example:

A jacket with 800FP uses a batch of down that would be more compressible and traps more (warm) air than a jacket with 600FP.

The complication, however, is that a 800FP jacket is not necessarily warmer than the 600FP one. There are many factors, but the most important one is the fill weight.

Fill Weight * Fill Power = Warmth

Fill weight is simply how much Down is used in the jacket.

Since FP correlates to how much air can that batch of Down trap per unit, we can multiply FP with Fill weight to have a rough idea how warm it would be.

For Example:

Mountain Equipment K7: 800FP x 300g fill weight =240,000
Mountain Equipment Earthrise: 700FP x 155g fill weight =108,500

Now we can be more confident that K7 can be expected to be much warmer, even without going into the shop.

Try using this formula for your own down jacket as a reference point to have an idea how warm other jackets would be!

Be careful that you should look at the Fill Weight, instead of the Net Weight of the jacket. The Net Weight is the final product weight, which includes the fabric, different features, zip etc. things that does not necessarily make it warmer but maybe more robust or convenient to use.

Speaking of which, where can I find these detailed information?

Finding information: Online, Label, On the Sleeve?

The obvious answer is to check the official website. Most outdoor brands would list at least the fill power under the specification, a lot of them would list the Fill Weight as well. If none of them exists, chances are you are looking at a synthetic jacket instead, or that product is not really made for the outdoors, or that brand is a bit dodgy.

When you walk up to a jacket in store, there is usually these information on its label and material tag.

A lot of of them also has its FP marked on one of the sleeves or hem, so people can immediately know what they are looking at in general.

Summery and Thankyou!

We have now talked about what does FP and Fill Weight means, how it relates to the warmth of a jacket, and where to find these information.

But there are much more to learn about down jackets, and I will make other posts on them.

Read the next post in the series about an important factor for warmth : Down to Feather Ratio!

Let me know in the comments if you have any questions, and tell your gear geeks to impress them!

See you next time!