Denier refers to the actual weight of the fiber. It is the weight, in grams, of 9,000 meters of the fiber. A 400 denier fiber weighs 400 grams for every 9,000 meters. a 1600 denier fiber is four times the weight (and, assuming the same density, twice as thick).
Denier correlates roughly with strength of the fiber. However, it generally has almost nothing to do with any actual properties of a *fabric*. The weave of the fabric, how many fibers are stranded into actual fabric filaments, etc. For example, a jacket can be made of "40 denier nylon" but still be 'tougher' than a jacket made of "400 denier nylon." 40 denier nylon can be stranded into 400 denier *threads* which will be stronger and more abrasion-resistant than a single 400 denier fiber.
Clear? Thought so.
What you can more or less take to the bank is that a very large denier nylon fabric (ie 1000) will feel much coarser to the touch than a smaller denier (ie 40) one.. but the denier measurement alone tells you almost nothing useful in terms of durability or strength.
