Duvet

A duvet is a type of bedding used as a blanket, on a bed. They are normally made of a cotton cover, filled with feathers and down or man-made fibres such as polyester, microfibre and hollowfibre. They are soft and comfortable, and keeps the person who's under it warm when sleeping. Additional bed throws (sometimes called a 'snug') may be added in the autumn/fall to add an extra layer of warmth. 
Togs.
The thickness of the duvet is measured by a tog rating. The higher the tog, the warmer the duvet will be. The warmest duvet on the market is currently a 15 tog. Most people who have heated houses will use a 4.5 tog duvet all year round, but sometimes in the autumn/winter people will upgrade to either a 7.0 or a 9.0 tog.