for spring and autumn; snapped together, 13.5 togs is designed for winter. Manufacturers may also offer up to 15 tog duvets. In some countries, such as France, the warmth of a duvet is rated in grams per square metre (g/m2) instead of togs. The two systems are incompatible because, for example, a 250 g/m2 polyester filling and a 250 g/m2 feather filling have the same weight but offer different levels of thermal insulation and therefore different tog ratings. However, typical all-season sets are sold as a pair of 200 g/m2 and 300 g/m2 duvets, creating a combined 500 g/m2 winter duvet, which would therefore be expected to match 13.5 togs. Standards and sizes Modern manufacturing conventions have resulted in a large number of sizes and standards. In popular culture In the story The Princess and the Pea, published in 1835, H.C. Andersen wrote about a princess lying on ten eiderdown duvets. The term "duvet day" is used in some countries to describe an allowance of one or more days a year when employees can simply phone in and say that they are not coming in to work, even though they have no leave booked and are not ill. The provision of this benefit became fashionable in the late 1990s with many larger companies in the UK. In the 1999 American film Fight Club, Tyler Durden regards duvets as pretentious blankets:Do you know what a duvet is? [...] It’s a blanket. It’s just a blanket. Then why do guys like you and I know what a duvet is? Is this essential to our survival in the hunter-gatherer sense of the word? No. See also Fill power Futon Silk comforter References External links Blankets