Is 840 denier nylon or 420 denier nylon stronger?

Denier nylon is a unit of measuring the thickness/weight of a thinly spun fiber. It indicates the material's durability, plus the fineness of fiber filaments and yarns - both natural and synthetic. The higher the denier, the thicker the fiber; the lower the denier, the finer the fiber. per Wiki answer to what is denier.