Tog is a measure of warmth (not comfort) of an item of bedding, especially duvets. It is a quintessential English standard of measure not found in other parts of the world.

Wikipedia has the following to say about it:

The tog is a measure of thermal resistance, commonly used in the textile industry, and often seen quoted on, for example, duvets and carpet underlay.

The word may come from toga, a Roman garment from which the English slang togs (meaning clothes) is probably derived. The basic unit of insulation coefficient is the RSI, (1 m² K / watt). 1 tog = 0.1 RSI.

The Shirley Institute in Britain developed the tog as an easy-to-follow alternative to the SI unit of m2K/W. Launched in the 1960s, the Shirley Togmetre is the standard apparatus for rating thermal resistance of textiles, commonly known as the Tog Test. A tog is 0.1 m2K/W.

In other words, the thermal resistance in togs is equal to ten times the temperature difference (in °C) between the two surfaces of a material, when the flow of heat is equal to one watt per square metre.


According to British retailer John Lewis, tog guidelines for duvets are as follows:

Lightweight summer duvet:
4.5 tog

Spring/Autumn weight duvet:
9.0 – 10.5 tog

Winter weight duvet:
12.0 – 13.5 tog

The tog rating of an item is therefore affected by a number of factors, not least the type of fibre under consideration. Apparently, the material with one of the highest tog rating is bubble wrap and one of the lowest is cement.  Some manufacturers of wool duvets maintain that tog ratings should only be applied to synthetic fibre and not natural fibres like wool. We are happy to go with the flow.  Our standard Southdown duvets contain 350gr of pure wool per square metre of duvet.

This equates to a 7.4 tog which presents an all-weather, all-year duvet most commonly sold, for example, in Germany.

Our reasoning behind an all-purpose duvet is simple – we don’t expect our customers to have buy two duvets of differing weights to get a decent night’s sleep all year round or to have to buy two light weight duvets and then have to Velcro them together in winter.

Over the years we have also listened to our customers, all of whom have different sleep needs. We therefore offer two other tog rated duvets – our Lambkin Lites at 4 tog (200gr of wool per square metre of duvet) and our Woolly Mammoth at 8 – 10 tog (500gr per square metre of duvet).

But before you decide what tog is good for you, consider another important factor and that is that tog measures thermal resistance and not levels of comfort which, with duvets, are two totally different things. Can you imagine trying to sleep under bubble wrap or cement?

Thus a very warm duvet with a 13.5 tog might appear to be ideal but can turn out to be very heavy if its alpaca, for example, or it might result in disturbing night sweats if it’s synthetic. This is why our Woolly Mammoths are capped at a 8 – 10 tog – anything heavier might become oppressive and just too much of a good thing.

Furthermore, a feather/down duvet with a medium tog might offer the right warmth but the fill might clump,and cause hot and cold spots in the duvet or aggravate asthma or allergies. The feathers over time will also breakdown and attract dustmites.

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