A tog is a unit of thermal resistance that measures how well a duvet stops body heat escaping. The higher the tog, the warmer the duvet. UK duvets run from 1 tog, for hot summer nights, to 15 tog, for cold winter bedrooms. Tog tells you warmth only: it doesn't measure weight, thickness or quality.
Here are the 7 common duvet tog ratings and what each one is for:
| Tog | Warmth | Use it for |
|---|---|---|
| 1 | Very light | Heatwaves and hot sleepers |
| 2.5 | Light | Warm summer nights |
| 4.5 | Summer weight | Summer and warm bedrooms |
| 7.5 | Light all-season | Spring and autumn |
| 10.5 | All-season | Most of the year in a heated home |
| 13.5 | Winter weight | Winter, rooms that cool at night |
| 15 | Warmest | Cold or unheated bedrooms |
What does tog stand for?
Tog doesn't stand for anything. It's a made-up unit, named after "togs", the British slang for clothes. It was devised at the Shirley Institute, a textile research centre in Manchester, as a simple way to describe how warm a fabric or filling is.
Technically, 1 tog equals a thermal resistance of 0.1 square metre kelvin per watt. In plain terms, every step up in tog means the duvet lets less of your body heat pass through it.
How is tog measured?
Tog is measured in a laboratory by placing the duvet over a heated plate and recording how much heat passes through it. The less heat that escapes, the higher the tog rating. Because the test is standard, a 10.5 tog from one brand should feel about as warm as a 10.5 tog from another.
What the test can't account for is your bedroom. A 10.5 tog duvet feels warmer in a centrally heated flat than in an old stone cottage, which is why the right tog depends on your room as much as the season. Our duvet tog guide for each season matches togs to rooms, and our page on the best winter duvet tog covers 10.5, 13.5 and 15 tog in detail.
Does a higher tog mean a heavier duvet?
No, a higher tog doesn't have to mean a heavier duvet. Tog measures how much warm air the filling traps, and a lofty filling can trap a lot of air while weighing very little. Hollowfibre and down both achieve high togs at a low weight. Dense, cheap fillings need more weight to reach the same tog.
A higher tog duvet is usually thicker, though, because more loft means more trapped air. Our microfibre duvet in 1 to 15 tog weighs between about 1.2 kg and 2.2 kg depending on size, with hollowfibre filling that traps warm air the way down does. It comes in all 7 togs in the table above, with 1 tog in double and king only.
Children need a lower tog than adults in the same room. Our guide to what tog duvet suits a toddler covers the 4.5, 7.5 and 9 tog options.
Written by the Adam Home team at Ensor Mill, Rochdale.
