In conclusion, it’s very easy to understand why you shouldn’t
purchase clothes without a UPF Rating. The Sun Protective Factory felt so strongly about this, in the 1990s, when the FDA discontinued regulating sun protective clothing, the Solar Protective Factory took the lead in developing performance durability testing standards by working with the American Society for Testing and Materials (ATSM). The CEO of SPF served as the chairman of the ASTM committee, working with the Federal Trade Commission (FTC) and the Consumer Product Safety Commission (CPSC) to establish UPF protocols and label standards with are presently used in the United States. SPF ratings, in our opinion, were meant to rate sun screens you apply to the skin, they give absolutely no information about the rating of the fabric, therefore it's not a factor that will benefit you in knowing anything about the ability of the fabric to block UV rays.
Our recommendation for our customers and readers is to NOT purchase any sun protective clothing item that does not include a UPF Rating and you may run across them when shopping for sun protective fabrics, although it is rare. It's also a good idea to look for seals of approval from organizations such as The Melanoma International Foundation and The Skin Cancer Foundation.
It's easy to remember!
UPF is for fabrics
SPF is for skin applications
All source information is from the International UV Testing Laboratories