What's the plural form of milled peat? Here's the word you're looking for.
Answer
The noun milled peat can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be milled peat.
However, in more specific contexts, the plural form can also be milled peats e.g. in reference to various types of milled peats
or a collection of milled peats.