UPF stands for Ultraviolet Protection Factor and indicates how much of the sun's UV radiation is absorbed.  UPF measurements of fabrics are generally tested by spectrophotometer equipment.  For example, a fabric with a UPF rating of 50 only allows 1/50th of the sun's UV radiation to pass through it. This means that this fabric will reduce your skin's UV radiation exposure by 50 times (98% UV block) in areas where the skin is protected by the fabric.  One big advantage of the UPF standard is that both UVAANDUVB rays are measured.  Our fabric has been tested to repel 99% of the sun's UV radiation with a UPF rating of 55+.  UV-Blocker umbrellas provide the highest protection available in the market. A copy of this certification is availabble upon request.