WPI (Whey Protein Isolate) are protein powders where the primary / only source of protein found within is whey protein isolate. WPI is a high quality, fast absorbing source of protein perfect to take when you need a quick hit of protein such as immediately post-workout or first thing in the morning when you wake up.
WPI contains little to no lactose, making it a perfect alternative for people who have issues with dairy to try. Due to the rapid absorption, it's extremely light on the stomach and won't cause any bloating. WPI also tends to contain more protein per serve, emphasizing its high quality and higher price than traditional protein blends.