Captain George Cocke, whose wife was from Danzig. Paul Rycaut was among the first to try and promote the duvet in England. Around 1700, he sent six-pound bags of down to his friends with instructions, warning that "the coverlet must be quilted high and in large panes, or otherwise it will not be warme". He also tried to sell them without success. In the mid-18th century, Thomas Nugent, an Englishman on a grand tour then passing through Westphalia, observed with surprise: Feather coverings came to be used in England in the mid-19th century, just as feather mattresses became common, and were unsurprisingly known as "continental quilts". They were not, however, universal. Of a British traveller in Germany in the 1930s, it was said that "She even learned to like feather quilts ('they don't seem to know about blankets – perhaps they didn't have them in the middle ages')". Duvets remained uncommon in Britain until the 1960s. Duvets are the most common form of bed covering, especially in northern Europe. They became popular throughout the world in the late 20th century. Description A modern duvet, like a sleeping bag, may be filled with down or feathers of various quality and cost, or silk, wool, cotton, or artificial fibers such as polyester batting. Duvets can reduce the complexity of making a bed, as they can be used without a top sheet, blankets or quilts or other bed covers. Duvets can be made warmer than blankets without becoming heavy. The duvet itself fits into a specially made cover, usually of cotton or a cotton-polyester blend. The duvet cover can be removed and laundered as often as the bottom sheet and pillow cases. The duvet itself may be cleaned much more rarely, and depending on its contents, may require specialist dry cleaning. While a comforter is fundamentally the same as a duvet in terms of construction, it is used somewhat differently. In the United States, comforters are used on top of the flat sheet, often without a cover. Thermal performance (tog rating) Manufacturers rate the performance of their duvets in togs, a measurement of thermal insulation. This enables the purchaser to select a duvet appropriate to the season: the higher the tog rating, the warmer the duvet. A few manufacturers have marketed combined duvet set consisting of one 4.5 tog and one 9.0 tog. The light-weight one is for summer and the medium one