Insulation Class is the insulation guarding the electrical portions of the motor. This avoids contact with other electrical parts and them interfering with each other.
The insulation is rated based on it’s resistance.
Common Insulation classifications are:
A – 105C
B – 130C
F – 155C
H – 180C
A common rule for selecting Insulation Class for motors is every 10C increase in operating temp cuts your insulation life by 50%