Material world is a cloudlike illusion

It is a fact that the material world is a great illusion because everything appears to be a tangible reality but at the next moment evaporates like the dashing foam of the sea or a cloud in the sky.

Similarly, the Absolute Truth, which is compared to the sky, remains eternally, and the temporary cloudlike illusion comes and goes away. Foolish living beings are attracted by the temporary cloud, but intelligent men are more concerned with the eternal sky with all its variegatedness.

(SB 1.13.29 - Purport)