Whey Protein Isolate (WPI) is the purest form of whey protein that currently exists. WPI is costly to use, but rates among the best proteins that money can buy. That's why it's the first ingredient you read on the Gold Standard 100% Whey label. This superior quality powder has been instantized for excellent mixability using a shaker cup or just a glass and spoon. There's no doubt that this is the standard by which all other whey proteins are measured.