Fill power describes loft per unit of down; it does not reveal how much insulation is inside the whole jacket. Fit, shell and construction also matter.
Separate fill power from the amount of fill
Fill power is a laboratory measure of how much space a set weight of down occupies when it lofts. Higher numbers can indicate more insulation efficiency for the same down weight and can help make a jacket lighter or more packable. They are not a temperature rating for the finished coat.
Fill weight answers a different question: how much insulating material is used. REI points out that a high-fill-power jacket containing very little down need not be warmer than a lower-fill-power jacket containing substantially more. Distribution across the body, baffle design, shell and layers also affect the result.
If a listing gives only “800 fill” but no fill weight, mark the total insulation as unknown. If it gives neither figure, the product photo cannot supply them. A visibly thick coat can still have different materials or construction than another coat of similar shape.
Apply these checks to the products in UIDBuy Down Jackets Spreadsheet.
Compare the jacket for the conditions you expect
Think about cold and dry use versus damp conditions before comparing two cards. Down is valued for warmth relative to weight and packability, but untreated down loses loft when wet. Synthetic insulation generally handles moisture better, while different shell and water-resistant treatments can change how a jacket performs. The current listing must identify the actual materials; appearance alone cannot do that.
A useful comparison records insulation type, any stated fill power and fill weight, shell material, hood, cuffs and intended layering. If a claimed weather feature matters, look for a clear specification rather than inferring rain protection from a glossy fabric photo.
| Listing detail | What it helps answer | What remains unknown |
|---|---|---|
| Fill power | Loft efficiency of the stated down | Total warmth without fill amount and construction |
| Fill weight | Amount of insulation in the garment | How evenly it is placed |
| Shell and finish | Stated wind or moisture features | Real performance without trustworthy specifications |
| Garment measurements | Room for your usual layers | Comfort until tried on |
Use measurements, not a letter size alone
Choose a jacket you already wear comfortably over a sweater. Measure its chest width laid flat, shoulder width, sleeve and body length. Compare those numbers with the current listing’s measurements for the selected option. A size M in a slim jacket may have less layering room than a size M in a relaxed parka.
Consider where the hem and sleeves will sit when you move, whether the hood is useful with your normal layers, and whether a very close fit compresses insulation. If the listing lacks measurements, ask for the specific dimensions you need rather than asking whether the jacket is “true to size”.
Know what QC photos can verify
Warehouse images can help confirm the colour, ordered size label, zipper, cuffs, hood, visible seams and obvious stains or damage. Front and back views may reveal whether the received piece resembles the listed silhouette. Ask for a detail view if a closure or label is unclear.
A photo cannot reliably verify the fill material, fill power, fill weight, warmth or authenticity. A jacket may also look flatter immediately after compression. Do not use a photo of loft alone to decide that a numerical fill claim is true or false; compare it with the current specification and the item received.
Illustrative comparison: jacket A claims 800 fill power but gives no fill weight; jacket B states 650 fill power and a fill weight. The higher number on A does not establish that A is warmer. First decide which information is missing, then compare fit and construction for your intended use.
Check the parcel implication before choosing a bulky coat
A down jacket may compress for packing, but the actual shipping quote depends on the warehouse parcel dimensions, weight, packaging and eligible route. Do not assume a light garment means a low shipping charge if the packed carton is bulky. Keep the product decision and the later parcel estimate separate.
The strongest shortlist is the one with a confirmed option, usable measurements and material details, not simply the puffiest thumbnail. If a critical specification is absent, mark it as a question to resolve before paying.
For a worked example using parcel dimensions, see Dimensional Weight Calculator: Compare Parcel Weights.
References
UIDBuy Down Jackets Spreadsheet
Down Jackets: compare puffer and parka measurements, fill descriptions and shell details and snapshot prices, then verify the selected option on the current listing.