grammatical number - When can you pluralize uncountable nouns?

I have a two part question, the second depending on the answer of the first. I don't know if that is frowned upon, but I'm not sure how else to ask.

Foil is an uncountable noun so it is not pluralized, but is it correct to use the plural when referring to several kinds of foils? Just like fish is plural but some people refer to several species of fish as fishes?

For example,

That company makes aluminum foils

Meaning, they make many kinds of foils out of aluminum

If this is OK, then why is

"organic and inorganic matters"

wrong but

"organic and inorganic matter"

right?

There are several kinds of matter being referred to. It seems to be following the same rule.

Answer

Many nouns which are normally uncountable are potentially countable in certain contexts. It’s a matter not so much of grammar as of the nature of the object to which the noun refers. There can clearly be different kinds of foil, and that makes it possible to speak of foils. Matter is a concept that that lends itself less well to pluralisation, but the Corpus of Contemporary American English has this record:

A 1992 study estimated that CSOs release between four and fourteen
billion pounds of solids and organic matters on a yearly basis

nationwide.

Organic and inorganic matters might in some contexts be an unwise formulation, because it could be taken to mean ‘organic and inorganic topics’.

David Crystal comments on the pluralisation of uncountable nouns in the latest post on his blog.