Fill power describes down’s loft under a defined test; fill weight describes how much filling is used. Neither is the total weight of the jacket. A fill-power number alone cannot provide a reliable temperature rating or establish which complete jacket will be warmer.
Start with three different measurements
Patagonia distinguishes fill power from fill weight: the former describes loft, while the latter describes the amount of down used. REI also explains that fill power comes from a laboratory measurement of volume for a specified quantity of down. Neither definition describes the entire assembled jacket.
Keep a separate field for total garment mass. Shell fabric, lining, closures and other components are part of a finished jacket, so a product or parcel weight cannot be treated as the amount of down inside it.
| Specification | Question it answers | Information still needed |
|---|---|---|
| Fill power | How much loft does the tested down produce? | Filling quantity and jacket design |
| Fill weight | How much filling is used in the stated garment? | Size, composition and distribution |
| Total garment weight | How heavy is the complete stated item? | How much of it is insulation |
| Parcel weight | How heavy is the recorded shipping sample? | The garment and insulation specifications |
Read a fill-power number without turning it into a temperature
REI describes the familiar fill-power figure in terms of the lofted volume produced by an ounce of down. Higher loft can improve insulating efficiency, but the same explanation warns that the amount of down and other factors also affect the warmth of the final garment.
An 800-fill label therefore does not establish that a jacket is suitable for a particular temperature. Before making a comparison, find the insulation quantity and the relevant construction details. If a listing supplies only the larger-looking number, write down what remains unknown.
Worked comparison: match the scope before comparing insulation figures
Consider two fictional records: A states 800 fill power but no filling amount; B states 700 fill power and 140 g of filling for a named size. These examples illustrate missing information and are not warmth ratings.
B provides a filling amount, while A leaves it unknown. Before ranking either jacket, ask for the filling amount and composition for your selected size, then compare construction and intended use. The visible figures do not establish which complete jacket will be warmer. A warehouse parcel weight cannot fill the missing insulation field.
| Example record | Information available | What to request |
|---|---|---|
| A: 800 fill power; filling amount absent | A loft claim | Filling amount, composition and the size described |
| B: 700 fill power; 140 g for a named size | Loft and quantity claims with a size context | Figures for your selected size and construction details |
Construction and intended use still matter
Rab’s buying guide distinguishes jackets through baffle construction, outer fabrics, features and intended activities. It also separates waterproof designs from other insulated jackets. These are product-design distinctions, not qualities that follow automatically from a fill-power number.
When researching a listing, look for a clear explanation of the hood, cuffs, hem, closures and insulation distribution. Compare the garment dimensions with the layers you intend to wear. A close-up can help you understand visible seams, but it cannot establish the internal filling quantity or certify a weather-protection claim.
Ask for the actual specification if the listing claims waterproof performance. Do not substitute a glossy shell photograph or a general “winter” label for that information.
Why a compressed photo cannot measure fill power
IDFL explains that compression, transport and storage can affect the loft of a sample and that laboratory conditioning is part of evaluating it. Its technical note concerns fill-power testing; it does not make a photograph into a test method.
A jacket photographed after packing may look flatter than a product image. Record that visible difference, but do not assign a numerical fill-power result from it. Conversely, a very puffy photograph does not independently verify an advertised number. Keep a documented specification and a visible observation in separate columns.
Build a shortlist from answerable questions
Use four questions for each candidate: What is the claimed fill power? What filling quantity and composition are specified? Which size do the figures describe? What construction and weather-protection information is actually documented? Add the relevant dimensions before comparing fit.
If a seller cannot supply an answer that matters to your intended use, pause rather than replacing it with an assumption. This is especially useful when two records have similar photographs but uneven specifications. The aim is a more complete comparison, not a universal warmth ranking.
For further research, open the down-jacket category and use the separate QC guide to identify useful photographic evidence. Current availability, option details and final prices still need confirmation on the external order page.
Frequently asked questions
Is an 800-fill jacket always warmer than a 700-fill jacket?
Not from those numbers alone. Insulation quantity, distribution and the rest of the garment affect the result. Obtain comparable specifications before deciding what the higher number means for the complete jacket.
Is fill weight the same as jacket weight?
No. Filling weight concerns the insulation. A complete garment includes other components, and a shipping sample may also include packaging. Check which quantity the listing actually names.
Can a QC photograph confirm a down-performance claim?
A photograph can show visible labels and construction. It cannot independently perform a loft test, establish the internal filling quantity or certify a temperature rating. Request the supporting specification for the exact product.
Related guides
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FABRIC EXPLAINEDWhat hoodie GSM tells you
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