And remember, the weight of the duvet does not relate to its tog rating. Duvets filled with feathers or down naturally have better thermal properties than synthetic versions. This means you don’t need as much filling to achieve the same rating, often making them lighter. Silk duvets can’t be measured by tog so they’re measured in grams of silk per square metre (gsm). Roughly, a 250gsm filling is the same as a 2-4 tog rating, 400gsm is about a 7-9 tog rating, while 600gsm is equivalent to 10-13 tog. The scale ranges from 1 tog (the coolest) to 15 tog (the warmest). For summer, you need a 1-7 tog duvet, whereas 10.5 tog or above is ideal for winter. Buying multiple duvets may not be realistic though, so getting around a 10 tog duvet to use all year is a good compromise. There are all-season options available too, but there’s more on this type later.