What Causes the Different Shapes of Clouds?

Clouds change shape because of how water moves in the sky. Imagine you're playing with balloons, when it's warm, the balloon expands and gets bigger; when it cools down, it shrinks. Clouds work like that too! If the air is warm and rising, clouds grow fluffy and puffy. But if the air is cool or moving fast, they stretch out into long lines or wisps.