What is the collective noun for sheets?

There isn't a specific, widely accepted collective noun for sheets.

You could use more general terms like:

* Set of sheets

* Pile of sheets

* Bundle of sheets

* Stack of sheets

If you're being creative, you could invent your own:

* Slumber of sheets

* Blanket of sheets

Ultimately, the best choice will depend on the context and the image you want to convey.