Tog (unit)
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. There is also a clo clothing unit equivalent to 0.155 RSI or 1.55 tog [1] 1 tog is roughly equivalent to the insulation provided by one broad sheet newspaper in dry conditions.
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 Togmeter 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:[2]
| Lightweight summer duvet: | 4.5 tog |
| Spring/Autumn weight duvet: | 9.0 - 10.5 tog |
| Winter weight duvet: | 12.0 - 13.5 tog |
A few enterprising manufacturers have marketed combined duvet sets consisting of two duvets; one of approximately 4.5 tog and one of approximately 9.5 tog. These can be used individually as summer (4.5 tog) and spring/autumn (9.5 tog). When joined together using press studs around the edges, or Velcro strips across each of the corners, they become a 14 tog winter duvet and as such can be made to suit all seasons.
Notes
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