---
title: "Fill Power (Down)"
description: "What down fill power is and how it differs from duvet TOG thermal resistance ratings used in UK bedding."
url: "https://bedguide.co.uk/glossary/fill-power/"
category: "glossary"
primary_entity: "fill power"
date_published: 2026-08-03
date_modified: 2026-08-03
---

# Fill Power (Down)

> Fill power is a loft-efficiency rating for down. Higher numbers mean more loft volume from the same mass of down. It is not the same as TOG, which measures a finished duvet’s thermal resistance. Synthetic hollowfibre fills do not use fill power. They rely on fibre geometry instead. Compare down quality with fill power, then check TOG for warmth.

**Definition.** Fill power measures how many cubic inches one ounce of down lofts under a standard test. Higher fill power means more loft per mass of down.

Also called: down fill power.

Fill power describes loft efficiency of down clusters. Pair it with
[duvet fill and TOG](/bedding/duvets-fill-and-tog) when reading product specs.
Warmth band still comes from the finished TOG test.

---

Source: https://bedguide.co.uk/glossary/fill-power/ · BedGuide — educational encyclopedia, no affiliate commission. Facts checked against official sources where possible; see https://bedguide.co.uk/editorial-policy. Report an error: https://bedguide.co.uk/corrections.