Critical particle sizes in semiconductor manufacturing are now below 5 nm, but the three SEMI standards for rating sub-50 nm UPW filters (C79, C82, and C89) can produce conflicting results. This presentation shares findings from a SEMI UPW Task Force white paper comparing these methods and offering guidance on method selection. It examines the gap between laboratory filter ratings and real-world performance, and concludes that C79 offers the clearest link to field contamination and start-up behavior in UPW systems.