Large fluffy clouds are formed when warm, moist air rises and cools. As the air cools, its ability to hold water vapor decreases, and the water vapor condenses into tiny water droplets or ice crystals. These water droplets or ice crystals then collide with each other and stick together, forming larger and larger droplets or ice crystals until they become visible as clouds. The type of cloud that forms depends on the temperature and moisture content of the air, as well as the amount of lift available to the air.