Is it correct to write "a 5-mm-thick layer"?

Question

Do I need hyphens? Should I use the indefinite article or zero article?

Answer 1

You can simply say 5 mm thick layer, no hyphens needed

Answer 2

Yes, to create a hyphenated adjective for the noun "layer" that includes numbers, you use the dashes. Another example: "the ten-year-old child", though you would otherwise say "the child is ten years old". As for the preceding article, since the noun "layer" is singular and countable, you would never use a Zero article, but either the/a (depending on whether it's definite or indefinite in this context). Zero article marks indefinite plural or non-count nouns ONLY.