Which cloud formation is often associated with being piled up, resembling cotton?

Cumulus clouds are characterized by their fluffy, white appearance and puffy shapes, resembling cotton balls piled up in the sky. These clouds usually form when warm air rises, cools, and produces condensation. The significant vertical development of cumulus clouds can result in a puffy, dome-like structure that stands out against the blue of the sky, particularly on sunny days. Because of their cotton-like appearance and their association with fair weather, cumulus clouds are often one of the first types of clouds that people recognize and describe.

In contrast, stratus clouds appear as a uniform gray layer that can cover the entire sky, typically bringing overcast conditions. Nimbus clouds are often part of the terminology referring to rain clouds, particularly cumulonimbus, which are not cotton-like but rather dense and dark. Altostratus clouds are a bit different in that they are typically gray or blue and often cover the sky in a uniform layer, but they lack the puffy, voluminous appearance of cumulus clouds. This distinction in structure and appearance helps clarify why cumulus is the correct answer for this question.