The highest tog duvet rating is typically 15.0. Higher tog duvets are best for winter when you need extra warmth, but they can also be used all year round if you are a cold sleeper who likes to stay cozy. However, its important to consider your own sleeping preferences and the temperature of your bedroom when choosing a duvet tog rating. Its worth noting that children should not sleep under anything warmer than a 10.5 tog duvet.