Duvets, Fill Power and TOG Ratings
Published 2026-08-03. Last updated 2026-08-28. Desk research by Kaiser Khan — we have not product-tested duvet fill and TOG. This is not a shop review and not medical advice.
In short
TOG measures how warm a duvet is: higher TOG means more insulation. Fill power describes how much loft down gives per weight — a quality score for natural fills, not a TOG substitute. Natural fills use down and feather. Synthetics use hollowfibre or microfibre. Pick TOG for room climate and fill type for loft, weight and allergy needs.
- TOG
- Higher = warmer
- Fill power
- Down loft only
- Common UK shop bands
- 4.5 / 10.5 / 13.5
- Duvet size
- Match the plan
Insulation of the finished duvet. Not a quality score.
How much loft a mass of down gives. Not a TOG substitute.
Summer, mid-range and cold-room starting points.
A UK King mattress is 150 × 200 cm. Read the pack centimetres.
About 4 minutes to read
What does TOG mean on a UK duvet?
TOG is a warmth rating. It measures how well the duvet resists heat flow. A higher TOG means more insulation. It does not mean better quality. A cheap 13.5 TOG duvet can be warmer than an expensive 4.5 TOG duvet. That is the point of the scale.
See the short definition in TOG rating. TOG is about the finished duvet. It is not fill power.
Which TOG should I use in a UK bedroom?
There is no single correct winter number. Room temperature and how hot you sleep matter more than a rule. Common UK shop bands are a useful start, not a medical prescription.
| Approx. TOG | Typical seasonal use |
|---|---|
| ~1–4.5 | Warm rooms / summer |
| ~7–10.5 | Mid-season / many year-round uses |
| ~13.5+ | Cold rooms / winter |
A 10.5 TOG is a common all-season middle. A 13.5 TOG is a common cold-room pick. A 4.5 TOG suits a warm room. If you and a partner disagree, two duvets or a dual-TOG setup can be kinder than one “compromise” that suits nobody.
Hot sleepers should also look at hot sleeper bedroom setup. Electric over-blankets are a different product — see electric blankets.
Is fill power the same as TOG?
No. Fill power describes how much loft a mass of down gives. It is a down quality idea, not a warmth rating of the finished duvet. A high fill-power down can reach a high TOG with less fill weight. That can feel lighter on the body.
Synthetic fills do not use fill power. They use fibre shape. Comparing a hollowfibre duvet’s “fill power” to down is a category error.
Fill weight (grams in the shell) is a third number. More grams can mean more warmth, or just a heavier, flatter pack. Read TOG for warmth. Read fill power only on down. Read weight if you care how heavy the duvet feels.
Should I pick down, feather or hollowfibre?
Down clusters trap air well and squash small for storage. Feather has quills and is heavier; it is often blended with down. Hollowfibre and microfibre are synthetic. They are often easier to wash at home.
| Fill class | Structure idea | Plain notes |
|---|---|---|
| Down | Soft clusters under feathers | Loft efficiency via fill power |
| Feather | Quills with vane | Heavier; often blended with down |
| Hollowfibre | Tubular synthetic fibres | Washable loft; no fill power rating |
| Microfibre | Fine synthetic fibres | Soft feel; denser packs possible |
Allergy needs are personal. A washable synthetic or a tightly woven cover can be a practical control. That is not a diagnosis. See allergy-friendly sleep system and washing bedding and pillows.
What size duvet fits a UK mattress?
Match the mattress centimetres first. A UK King mattress is 150 × 200 cm. Many “King” duvets are cut larger so they drape over the sides. Overhang is a comfort choice. It is not a size error.
If your mattress is EU 160 × 200 cm, a UK King duvet may look short on width. See UK vs EU sizes. Sheets are a separate SKU — bed sheets materials.
Is a comforter the same as a duvet?
In UK usage a duvet sits inside a cover you wash. “Comforter” is more common in US shops for a finished quilted top layer. Always check whether a cover is needed. Buying the wrong system wastes a SKU, not a night of science.
Related BedGuide entries
How it works
Frequently asked questions
What is the best TOG rating for winter?
Many UK households use about 13.5 TOG or higher for cold bedrooms. 10.5 TOG is a common all-season middle. 4.5 TOG suits warmer rooms. Room temperature and personal preference matter more than one fixed winter number.
Is fill power the same as TOG?
No. Fill power measures how lofted a mass of down is. TOG measures the finished duvet's warmth. A high fill-power down duvet can reach high TOG with less fill weight.
Down versus hollowfibre — what differs?
Down clusters trap air well and squash small. Hollowfibre and microfibre use synthetic fibre shapes for loft and are often easier to wash. Allergy and care needs drive many choices.
What size duvet fits a UK King mattress?
Match the duvet to the mattress centimetres, then decide if you want overhang. A UK King mattress is 150 × 200 cm. Many UK King duvets are cut larger so they drape. Check the duvet’s own centimetre label.