Any coated lenses need to be treated with care. Usually, the cloth you use isn't the problem: it's the dust and grit that you grind between the cloth and lens that does the damage. The best way to clean any lens is to first rinse it with warm water. This will remove the sand and dust. After a quick rinse, dry the lenses with a lint-free microfiber cloth. It's important to remember that the cloth also needs to be protected from sand and dust. If you paid real money for your awesome sunglasses, make sure you keep a convenient cleaning cloth in a zipper bag.