TOG measures how well fabric retains heat so it tells you how warm the sleep sack will be for your baby. The higher the TOG, the warmer the sleep sack. Here is a handy TOG guide for more info.  Recommended TOG depends on (1) nursery temperature and (2) how hot your baby tends to sleep.  - TOG 0.8 is suitable for spring / summer and warmer nurseries between 67 - 75 degrees. Also suitable for hot sleepers.  - TOG 1.2 is suitable for most nurseries between 64 - 72 degrees and offers versatile four-season warmth. It’s our bread-and-butter TOG.  - TOG 1.5 is suitable for fall / winter, and cooler nurseries between 61 - 69 degrees. Also suitable for cold sleepers.  Tealbee’s TOG is lab-tested and accurate (many other brands can’t say the same!).