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Before purchasing a duvet, remember to check its tog rating. The "tog" is a measure of thermal resistance -- that is, how hard it is for heat to escape through the duvet. A 3.0 - 4.5 tog rating is usually sufficient for summer. For spring and autumn, a rating of 7.0 to 10.5 will keep you warm. In winter, you will probably prefer a duvet with a tog rating of 12.0 to 13.5. If you are buying a duvet for a child, go for a lighter tog rating -- children are more likely than adults to find a high-tog duvet uncomfortably warm. If you want to be prepared for anything, look into duo duvet sets. These include both a low-tog and a medium-tog duvet, which can be joined together to create a high-tog winter duvet. Some manufacturers also offer duvets that have different tog ratings in each half, for the benefit of partners who feel the cold unequally.
The exterior of the duvet can be of several different fabrics, but polyester, polyester/cotton blend, silk, pure cotton, and polypropylene are the most common. As with other bedclothing, natural fabrics tend to be the most comfortable and luxurious. Polyester/cotton blend strikes a good balance of comfort and durability.
You should also consider whether you want a natural filling (i.e. duck or goose down or silk) or a synthetic filling. Each has its own pros and cons. Natural-filled duvets are lighter in weight and tend to last longer than synthetic-filled ones -- as much as 30 years as compared to 10 years for synthetic fill. As against that, natural duvets cannot be washed at home, since the filling must be dried completely, which is difficult to achieve with a home dryer. Some people also have allergic reactions to the feathers in natural fill.
Synthetic-filled duvets are, as mentioned above, heavier and have a shorter lifespan. However, you can wash them at home if your machine is large enough, and their filling is hypoallergenic.
Once you have purchased your duvets, consider whether you also want to buy duvet covers to protect them. While this does add to the weight and expense, duvet covers also help to extend your duvets' lifespan. If you have chosen natural fill, duvet covers are strongly recommended, in order to reduce the frequency with which you have to wash the duvet itself. Duvet covers can also be used, with the duvet removed, as light blankets in the summer.
