What is the collective noun for a group of flour?

There isn't a specific collective noun for a group of flour. Flour is a powder, not a group of living creatures.

You could use some descriptive terms to indicate a large amount of flour:

* A sack of flour

* A bag of flour

* A barrel of flour

* A heap of flour

* A cloud of flour (if it's being thrown or stirred)

Ultimately, the best way to describe a group of flour depends on the context and the image you're trying to create.