The summer duvet is very different from the winter duvet with significantly varied requirements for different times of the year. The most popular form of summer duvet cover is the lightweight 4.5 tog which is the official measurement of the heat resistance of a summer duvet. There are other tog ranges which include 9.0 tog to 10.5 tog for the spring/autumn range and the winter duvet which comes in at a significantly higher 12.0 tog to 13.5 tog.
In simple terms, summer duvets are much better if they are able to retain less heat than winter duvets because you would expect the temperature to be higher in those long summer nights. Any duvet sets you buy will have a tog reference so that you can tell how much heat is retained and the difference in temperature between the outer surface of the duvet and the inner filling of the duvet.
In simple terms, the lower the tog rating the less heat is retained within the duvet set and the higher the tog rating the more heat is retained within the duvet.
