Fill power (FP) is the volume one ounce (about 30 g) of down occupies under a stated mass, in cubic inches. It is the international shorthand for how much still air that down can hold. Higher FP, more warmth per gram — if the garment actually contains that down, at that fill weight, in baffles that let it loft.
TrimGem treats fill power as a lab number with a method, not as a hoodie print.
How it is measured
GB/T 17685 defines down and the cylinder idea: ~30 g, a ~100 g platen, volume in cubic inches (or a centimetre height on a Chinese cylinder — the two are converted). GB/T 10288-2016 is the test method: steam restoration, IDFB-type instrument, a pour tube. Chinese results run a little below IDFB and closer to some Japan/Korea practice. Read three times, average.
Rough quality talk: 650+ is decent; 800+ is high; 1000 exists at the top. GB/T 45266-2025 uses fill power among other measures for a 1A–5A consumer grade story.
A hangtag “800 fill” means 800 in³ / 30 g. A conversion used with GB/T 14272 centimetre tables is of the form 800 × 0.0252 ≈ 20.2 cm on that cylinder — use the standard’s own table, not a café conversion.
FP is not the only warmth
Fill weight (grams of down in the garment) still matters. 20 g of 900-fill is a vest; 200 g of 550-fill is a parka. Climate talk (illustrative, not a medical claim):
- Mild (about −5 to 5 °C): lower FP or less fill can suffice.
- Cold: 600+ and enough grams.
- Severe: 800+ and a garment design (baffles, shell, hood) that is more than a number.
GB/T 14272-2021 ties minimum centimetre loft to cluster content and species (duck vs goose). Example shape of the table: higher cluster % → higher minimum cm; goose minima sit above duck at the same %. A 90% goose might be asked for ≥17.0 cm (≥675 cuin-equivalent on that conversion); a 75% duck sits lower. If the tag says 90% and the cylinder says 14 cm, the tag is the problem.
Trade groups have also published warmth grades mixing cluster %, FP and turbidity, and temperature bands (severe cold to cool). Use them if the customer named them.
Clo and “warmth retention”
Thermal resistance clo (1 clo ≈ comfort at 21 °C, 50% RH, 0.1 m/s air) and % warmth retention are how synthetic fills and treated downs get compared in a hot-plate lab. Far-infrared and PCM marketing often quotes clo at a stated gsm (see functional fills). Down programs should still lead with FP + cluster % + fill weight, then clo if a brand wants a comparable number across fibre types.
After wash and compression
Consumer tests (e.g. China Consumers Association on children’s down) find wash can dent FP without destroying a good lot. Repeated wash and vacuum compression that kinks barbules are how 800-fill becomes 600-fill in a warehouse. Spec unpack and recovery time.
Write method (GB/T 10288 / IDFB), cluster %, species, FP (cuin and/or cm), fill weight, and the garment’s climate claim. Fill power without grams is a balloon. Grams without fill power is a sack of feather fibre. Warmth is both, in a shell that lets the down loft.