SPF (Sun Protection Factor) is a UVB-only sun rating for sunscreens, only.Basically, SPF testing has some poor person stick their arm in UV light and the time until they get sunburned is measured. If that person sunburns in 5 minutes without sunscreen, but it takes ten times longer (50 minutes) with sunscreen, then that lotion is designated SPF 10. This is a measure of UVB (think burning rays and cancer), not UVA spectrum rays (think aging/skin damage and cancer rays) .Note that sunscreen manufacturers self-test their products without a standard test protocol or certification, and consumer reports found only 2 of 20 tested provided the SPF protection promised after water immersion, with 18 ranging from 4 - 50% less than claimed. The non-profit organization, The Environmental Working Group (The Environmental Water Group) does independent annual testing of sunscreen safety and effectiveness for UVA and UVB for thousands of sunscreens and is well worth checking.UPF (UV Protection Factor) is defined specifically for fabrics. It measures how much UVA and UVB radiation gets through the fabric barrier. Standard test procedures must be followed, as defined by several testing agencies (see next section). For example, UPF 50+ (the highest allowable rating) means less than 2% of the UV light gets through. UPF 30 means 1/30 = 3.33% of the incoming UV rays get through to you, etc. So higher UPF ratings have better UV protection.