Select your baby sleep sack based on the warmth level room temperatures. For hot and warmer climates in the USA, Use 0.5-1.0 TOG sleep sack for rooms 70°F and above, 1.5 TOG for 65-70°F, and colder USA climates choose the 2.5 TOG sleep sack fabric thickness for rooms under 65°F. Be sure to consider the air conditioner room temperature in mind when choosing the best sleep sack for your baby. This scientific TOG rating system ensures your baby stays perfectly comfortable warm year-round. A comfortable baby sleeping can improve their sleep duration and sleep quality.