Straw When it is said as "straw, wheat straw and straw", it is an uncountable noun.

For example, the straw in your question means "straw", so it is an uncountable noun, so it cannot be plural.

Straw When speaking through a straw, it is a countable noun.

A bottle of lemonade with a straw in it. A bottle of lemonade with a straw.

In addition, in some fixed phrases, the plural form is useful:

For example, catch straw, catch straw.