Essentially, the scientists coated the cotton fabric base with zinc oxide nanorods as well as zinc oxide crystallites, which Discovery describes as "dumbbell-shaped." That treated material was found to have a UV Protection Factor (UPF) rating of a whopping 101.15. To give you an idea of what that number means, UPF has a few different levels of UV protection. UPF 15-24 is "good," UPF 25-39 is "very good," and so on. The highest level is UPF 50 and up, which is considered "ultimate UV protection"--it lets in less than two percent of UV rays. A UPF of 101.15 lets in less than a single percent, which would qualify for "excessive" protection if that level existed.