The phrase "thick coat" is correct and can be used in written English.
For example, you could use it in the sentence, "She shivered in her thick coat as she ran through the snow."
"This one is really soft, thick coat.
Sparky's got a thick coat of fur, but is that enough?
They can sustain high body temperatures because of their thick coat of fur, the researchers suspected.
Maker hours blend childhood summer-day vagueness with a thick coat of artistic entitlement.
The parasites are covered by a thick coat of glycoprotein (a protein with sugars attached).
An insoluble, smooth and uniformly thick coat of calcium polysaccharide was formed around the core pellets.
It is surprisingly flavorless, with the thick coat of cornmeal overwhelming the meat within.
A thick coat of fog had dropped onto the Army base.
Mr. Muller wore glasses, a thick coat and a short beard.
Ivanka inherited her mother's canniness and added a thick coat of subtlety.
With his humble beret and thick coat, the artist is deeply drawn into a murky backdrop.
