What’s a tog?

I’m a big fan of James O’Brien’s Mystery Hour. Each week, members of the public call in with questions about almost anything which are then answered, or not, by almost anyone, provided they can explain how they know what they know. A couple of weeks ago, Marcus from Dundee asked ‘What does tog mean?‘ for duvets and blankets. Melvin provided a correct answer, that ‘Essentially, it tells you how quickly heat travels across the duvet.’. But the development of a the tog has a much richer history. And so this instalment is all about the tog, a tog-blog, if you will.

The internet is surprisingly patchy when it comes to in-depth information about the tog. There are various duvet manufacturers that tell us summer duvets are up to 5 tog, and the warmest winter duvets around 15 tog. The higher the tog, the warmer you are over night.

There’s a little more detail about the technical definition of the tog, in terms of its measure of thermal resistance. In fundamental S.I. units, a tog is 0.1 K/W.  Since there’s usually a big difference between skin temperature and room temperature at night time, your body loses heat to the surroundings. You feel cold if the rate of heat loss is too great. But, as this paper found, sudden infant death syndrome can be associated with overheating, so getting togs right is important.

The methods for measuring togs is outlined in British Standard 4745:2005, using the aptly named ‘togmeter’. You can watch the dreamy process here:

What the internet is almost totaly unhelpful with is the tog’s origin. Wikipedia mentions the Shirely Institute with no reference. This is corroborated by a 2007 Spectator article, Feather your nest, which again mentions the 1940s and the Shirley Insitute’s connection to British Cotton Industry Research Association. So, feeling adventurous, I called up the Memoirs from the institute from 1942-1946 to the British Library. The year range I chose was a total punt, but I got lucky.

Here, for the first time (as far as I know) in digitised form is the spectacular genesis of the tog.

The first description of the tog. The transmission of heat through textile fabrics - part II' p.343 by F. T. Peirce and W. H. Rees Shirley Institute Memoirs, Vol XXII 1944-1945  The first description of the tog. The transmission of heat through textile fabrics – part II’ p.343 by F. T. Peirce and W. H. Rees Shirley Institute Memoirs, Vol XXII 1944-1945

The paper was written by F. T. Peirce and W. H. Rees and published in the 1944-45 edition of the Memoirs. It’s an excellent example of the cultural and historical contingency of physical units – the equivalence of a tog to a ‘light summer suit’ demonstrates who was being borne in mind, and the mention of clothing too thick to fight in a sobering reminder of the times in which the tog was developed.

Published by

Harry Kennard

Energy, climate change and health researcher

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