Down Fill Power to Loft & Thermal Insulation Modeler

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 5 inputs are read from the form on every keystroke: Fill Power, Fill Weight, In-Garment Loft Factor, Insulated Area and Insulation per cm of Loft.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves In-Garment Loft Thickness together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Thermal Resistance, Thermal Resistance, Free Loft Volume, In-Garment Loft Volume and Fill Weight per m² — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

The tool loads with this case already solved — the In-Garment Loft Thickness shown above is its answer. Change one value and the difference from this baseline is the sensitivity of the result to that variable.

How to use it

1. Work through the input groups in order — Fill and Garment. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read In-Garment Loft Thickness in the dark results panel — that is the headline figure, expressed in cm.
4. Check the supporting rows underneath (Thermal Resistance, Thermal Resistance, Free Loft Volume, In-Garment Loft Volume and Fill Weight per m²) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing In-Garment Loft Thickness before a trial is booked, so machine time and material in Factory Physics & Assembly Logistics are committed against a calculated figure rather than an estimate.
• Costing and quotation — In-Garment Loft Thickness is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Fill Power) shows how much of the gap in In-Garment Loft Thickness each variable explains.
• Teaching and study — the accepted ranges bracket normal Factory Physics & Assembly Logistics practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Assumptions and limits

• Fill power is measured on conditioned down in a free cylinder; a real garment restricts it, which is what the loft factor carries. Loft that is compressed — at the shoulders under a pack strap, or anywhere the baffle is too shallow — insulates in proportion to its compressed thickness, not its nominal one.
• Every input is bounded to the range normal practice occupies (Fill Power 300 to 1000 cuin/oz, Fill Weight 10 to 2000 g and In-Garment Loft Factor 0.3 to 1 ×, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Questions people ask