A TOG rating is basically a measure of how well a fabric keeps the warmth in. This is important as a guide for keeping your baby safe and comfortable at night.
By understanding the TOG ratings, you can avoid overheating and make sure your baby is as warm and cozy. The warmest sleep sacks have the highest rating, so for example, a 2.5 TOG sleep sack is warmer than a 1 TOG sleep sack.