The difference between a size 16 and a size 16W is in the way the patterns are constructed. A size 16 is simply a scaled-up version of the same suit in a Womens size 2. For example, no changes are made to the proportions of the pattern, and a set amount of inches is added to each size. A size 16W, on the other hand, is considered a Plus Size swimsuit and is cut specifically to fit a curvier body. It may look like the same swimsuit that is available in a Womens size, but the proportions are somewhat different to ensure a flattering fit. The pattern is changed very slightly in order to make sure that the swimsuit has support where it's needed. There might be more room allotted in the bust area to accommodate fuller cup sizes, and the leg openings are usually cut lower. For the best possible fit, it is always recommended to check the size charts located on the specific product page.